Originally, (other than making S&L a strategic game) this was intended to be playable even only with the standard Snakes and Ladders, and Monopoly board game pieces, but the Monopoly mechanic adapted was eventually removed and this needed more components such as a sand timer and more dice…then turned into a more complicated gameplay mechanics about mountain climbing—which hopefully didn’t turn out badly.
The main difference this has with the S&L is that players get to decide which climber piece to move with which dice number. With regards to the Pandemic game, the overflow/outbreak mechanic was borrowed.
The post below still requires a lot of development specially in the mathematical department (e.g. how the number of players would change the gameplay, and how the number of snow cubes affects difficulty) but should be enough to explain the core gameplay mechanics. In advance, thanks for bearing with this lengthy post. 
GAME NAME
Mt. Highrime
INTENDED PLAYER EXPERIENCE
Strategic and cooperative turn-based game with a slice of frantic, time-pressured element.
Appreciate during the panic-stricken moments the cooperative strategy set into place.
Hopefully suits a family game.
CONCEPT OVERVIEW
The summit of Mount Highrime holds artifacts of unimaginable value. They lay covered at the peak, secured under the thickness of snow, guarded only by the harsh weather and frosted paths. The price is enormous. And the hike…costly.
Will its reward be worth its peril?
VICTORY CONDITION
As a team, reach the required amount of money with the total value of the artifacts recovered plus the cash in hand.
GAMEPLAY OVERVIEW
The whole gameplay is divided into three stages which happen sequentially: planning, ascent (pick-up), descent (delivery).
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Planning Overview
The players are given an amount of money to spend on whatever equipment or items they may need during the climb. But be cautious, since the cash unspent is added to the final amount of money required in winning, players wouldn’t want to spend more than they need. But you can never be sure, can you? -
Pick-Up Overview
The players must strategically (and luckily) climb up from tile 1 to tile 100 with as many climbers they can, and gather as many artifacts they can. The hazard: snow falls every turn; the longer they reach the top, the more dangerous the path to the summit…and back. -
Delivery Overview
The treasures are no good if they can’t return. The players must go back to tile 1 while avoiding the dangers of the icy mountain. If they take too long descending or tread a misstep…then the avalanche cometh!
GENERAL MECHANICS and RULES
Stage 1: Planning
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Buy items and equipment with the amount of money provided.
- The team of players is given limited amount of money to purchase items and equipment.
- Items are represented in cards and are varied and limited. They are generally consumable during gameplay.
- One example of items that will be used for this explanation is Tents.
- The unspent money is put aside and to be added later to the value of collected artifacts.
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The items are distributed to the players.
- Each player can only hold up to a certain number of cards.
- Items may only be used during the Ascent or Descent stages.
- Items may only be used by the player holding the card.
- Items may be passed by one player onto another player if at least one climber of each player shares the same tile.
Stage 2: Ascent
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The climbers ascend according to the dice roll.
- Each player controls two (2) climber tokens and has two (2) movement dice—which are just regular six-sided dice. (For clarification, “climbers” are different from “players”.)
- Each player plays during his turn then the turn passes on to the next player.
- For now, the S&L game board would serve as the Mount Highrime that climbers need to ascend.
- All climbers start at tile 1 and attempt to recover artifacts in tile 100.
- To move climbers, the active player rolls both dice. The number shown on the dice are the number of tiles the player needs to move his climber by ascending the numbered tiles (just like in S&L), but the player decides which climber uses which number on the dice. One dice for one climber only. The player uses one dice number to move one of his climber and the other dice number to move the other climber. The player must use both dice (unless overruled by an effect or something).
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Ladders represent hidden routes to climb the mountain faster.
- Snakes and ladders work similarly to the original game but with a few modifications.
- Ladders can only be used to go up if a climber ends its turn on the bottom end of the ladder and if that bottom end has a tent pitched. (Later in the game, a ladder can be used to go down if a climber ends its turn on the top end of the ladder and there’s a tent on that end.)
Below are some rules in pitching tents:- A tent is represented by a shelter token (inspired by Monopoly house pieces).
- Generally, a tent can be pitched on any tile other than the top end of the snake (the snake’s head). It is also possible to pitch more than one tent on the same tile. (Explanation later.)
- A tent can be pitched at the end of the player’s turn using a tent item card and then discarding it. (i.e.: The climber can pitch a tent on the tile after moving.)
- A tent may also be pitched at the start of the player’s turn after the dice are rolled, but that particular climber forfeits using a dice number to move and ends its turn. (i.e.: After the dice roll, the player chooses for each climber whether to ascend the mountain or pitch tent, but not both.)
- The ladder can be used only at the start of the player’s turn. This movement replaces the use of the dice for that particular climber. (i.e.: After the dice roll, the player decides for each climber whether to use the ladder or ascend the mountain, but not both.) This implies that a climber cannot pitch a tent then climb the ladder at the same turn.
- For strategic purposes, the player may opt not to ascend the hidden route.
- For clarification, after the climber uses the ladder, the climber can still pitch a tent at the top end of the ladder before ending its turn (thus, leaving one dice number unused).
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Snakes are slippery paths.
- If the climber ends it turn on a snake’s head, the climber piece immediately slides down to the other end of the snake (the snake’s tail).
- It is possible to have a tent pitched on the snake’s tail end. After the climber falls, if the snake’s tail does NOT have a pitched tent on its tile, then that particular climber (laid on its side) loses its next turn and returns into play after that next turn. If the snake’s tail has a pitched tent, that climber is not laid on its side after falling.
- If a climber loses its turn, then the player only rolls one dice for the remaining climber. If both climbers of a player lose turn, the snowfall phase still occurs before the player ends its turn (see Snowfall below).
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Snow fall after each player turn.
- Snowfall will slightly affect the difficulty of the ascent, but more significantly the descent.
- Snow is represented by small white cubes (inspired by Pandemic’s cubes) placed on the tiles.
- After each player’s turn, the player will add two (2) snow cubes on the board. Snow cubes are added following the rules below:
- The player rolls three (3) dice: one (1) red, and two (2) white.
- The red dice determines which row the snow cubes will be added while the white dice determines the columns. (i.e.: The two cubes will be on the same row as determined by the red dice.)
- The red dice corresponds to the row starting from the top of the board: row 1 being the row with tiles 100 to 91, row 2 has tiles 81 to 90, and so on until row 6 with tiles 41 to 50. (For clarification, snow cubes are not directly added on tiles 1 to 40.)
- Each white dice corresponds to one snow cube. After the snowfall dice roll, the white dice on the left (of the other dice) corresponds to the column number on the board when counting from the left, while the white dice on the right corresponds to the column number on the board when counting from the right.
- As an example, if the result of the three dice are 3-2-6 (which respectively correspond to red, left, and right dice), then the player places one cube on tile 79 (i.e., counting 3 rows from the top and 2 columns from the left) and also places one cube on tile 76 (i.e. counting 3 rows from the top and 6 columns from the right).
- Due to this rule, it is more likely to buildup snow cubes in the middle of the board. (Consider a result of 2-6-5 where the two cubes are both placed in tile 86.)
- A tile can contain a maximum of 3 snow cubes only. If a cube must be added to a snow-filled tile, that cube is added instead to the adjacent (same-row) tile with lower number. If that lower-numbered tile is also full, the cube is added instead to the adjacent tile with higher number. If both adjacent tiles are full, the cube is added instead on the tile under the initially intended tile. If that tile is also full, the rule above is applied until the cube is placed legally. This is called cascading.
- As an example, the priority placement sequence for tile 77 is 77, 76, 78, 64, 63, 65, 57, 56, and so on.
- As another example to emphasize same-row adjacency, the priority placement sequence for tile 91 is 91, 92, 90, 89, 71, 71, and so on.
- Pitched tents on a tile are removed if the tile receives three snow cubes. Also, tents cannot be placed on tiles with 3 cubes.
- After the snowfall phase, play passes to the next player.
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A climber at tile 100 may recover artifacts.
- If a climber reaches tile 100 (even with excess number on the dice), that climber must stay at tile 100 until the team decides to descend.
- After dice roll at the start of the turn, the player may choose to gather artifact/s with his climber/s at tile 100, forfeiting any other possible action choice for that climber.
- Each climber can only recover one artifact per turn.
- Artifacts are represented in cards. When a climber attempts to recover an artifact, the player draws the top card from the shuffled artifact deck.
- Each climber has a limited amount of artifacts it can carry.
- When the team is satisfied with their value of artifacts, the team declares moving on to stage 3, Descent.
Stage 3: Descent
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The climbers descend according to the dice roll.
- The dice roll and snowfall roll for this stage is similar as Ascent Stage’s but, instead of ascending the tiles, the climbers descend the tiles following the number on each tile. (All climbers will descend during this stage, whether it has reached tile 100 or not.)
- The goal of this stage is to bring all climbers back to tile 1.
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The ladder may be used to go down, the snake’s heads are still slippery.
- A ladder may be used to go down if a climber ends its turn on the top end of the ladder and there’s a tent on that end. A ladder cannot be used to go up during descent.
- The effect of landing on a snake’s head is still the same but with two additional consequences. First, if the climber landing on a snake’s head holds artifact/s, that climber loses one artifact whether or not the snake’s tail has a tent (his artifact cards turned face down, shuffled, and one card randomly removed). Second, landing on a slippery path triggers an avalanche (see below).
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Be careful and swift. The avalanche sweeps.
- The avalanche may be triggered in at least two ways: when the snow cascades, or when a climber slips.
- When an avalanche happens, the snow cubes from the tile that triggered the avalanche and all the tiles below it cascade by following the rules below:
- When an avalanche is triggered, all the cubes from the tile that triggered the avalanche are placed on the tile under it (thus, leaving no cube on the triggering tile). If the tile below it is full, follow the rules in cascading.
- After resolving the cubes from the triggering tile, every cube (but one) from every tile from every row below it will cascade. That is, one cube remains on each tile while the others cascade to the tile under it. This event is resolved from the highest numbered tile to the lowest. Nothing happens on the tile if it has one or no cube on it. If the tile below it is full, follow the rules in cascading.
- As an example, if tile 95 is full and one cube is to be added, the avalanche event is triggered. All four (4) cubes from tile 95 are placed on tile 86. But since tile 86 has 2 cubes and can only accommodate 1 more cube, the rules in cascading is observed. Then, every tile from tiles 90 to 11 (i.e. rows below tile 95) cascade their cubes to the tile under each of them but leaving one cube on each affected tile.
- As a similar example, if tile 95 only has one cube but a climber slips on it, then the avalanche event is triggered. The cube from tile 95 is placed on tile 86, still observing the rules in cascading. Then, tiles 90 to 11 cascade their cubes. (For clarification, if there are no cube in tile 95 but a climber slips on it, avalanche is still triggered.)
- If the tile receives 3 cubes and has tent/s pitched on it, remove all the tents.
- If the tile that must cascade down has a climber on it (meaning, the tile has at least 2 cubes), then the climber(s) goes down with it to the next row, loses its next turn (laid on its side), and loses one artifact if applicable. However, if that tile the climber is on has a tent pitched, then the climber is safe. (For clarification, if the tile that receives 3 cubes has both tents and climbers on it, then the tents are removed but the climbers are safe.)
- If tile 1 receives 3 cubes, then the game ends and the players lose.
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There is a difference between avalanche triggered by snowfall and from climbers slipping off.
- If the avalanche is triggered due to a climber slipping off, then the avalanche happens immediately after resolving the consequences of the climber placed on the snake’s tail.
- If the avalanche is triggered due to a snow-filled tile, then all the players are given one (1) minute to flee for safety to a tent before the avalanche comes.
- To start fleeing, the sand timer (with approximately 60 seconds) is turned over.
- Within the time limit, all players may roll their movement dice at the same time and move their climbers accordingly. The players may keep rolling-and-moving until they are satisfied with the tiles they landed on or until the time runs out.
- The players, as usual, roll two dice each but only the climbers under the triggering tile must be moved. That is, climbers on the same row or above the triggering tile are not moved. If the player does not have a climber under the avalanche line, then the player does not roll his dice. (For clarification, if the player’s climber is on the triggering tile, then that particular climber falls down with the cubes, loses its next turn (laid on its side), and loses one artifact if applicable.)
- This is an advantage for players with only one climber under the avalanche line: they have two dice and one climber to move, which means they may have two options to choose from (but not both) in moving one climber.
- The other movement rules are the same: one dice for one climber. If the player has two climbers below the avalanche line, then he needs to move both climbers according to the dice roll, even if one of the climbers is already safe in a tent and the other is not. Alternatively, the player may decide not to roll when one of his climbers is safe and rather risks the other climber’s safety.
- When a climber slips off while fleeing and the snake’s tail does not have a pitched tent, then the climber (laid on its side) loses its next turn, loses an artifact, and loses its opportunity to flee. Additionally, the player only rolls one dice for the remaining climber. Sliding down the routes with “tented” tails while fleeing may be a good strategy (because it won’t trigger an additional avalanche and the climber won’t lose a turn), but the climber still loses an artifact (which may be resolved later after the time runs out).
- Cards cannot be used during fleeing.
- The avalanche comes when the time runs out.
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The game ends when all climbers reach tile 1.
- If a climber reaches tile 1 (even with excess number on the dice), it is immediately removed from the board.
- If a player has one climber on tile 1 and the other climber still needs to move, the player still rolls two dice at the start of his turn and chooses only one dice number to use.
- Immediately after all climbers reach tile 1, the game ends. The value of the artifacts plus the cash in hand are summed up and verified if the target value is achieved.
- All players win if the target value is achieved. Otherwise, all lose.
I’ll just put the additional mechanics on the next post. 
EDIT: Improved some wordings.
