This is a thread for documenting obscure mechanics in Mario Party DS. I originally started this in the Discord but wanted to move it here for visibility.
You are encouraged to reply with questions as well as your own findings! Everything known so far will be added to the OP.
Spaces (all boards)
Duel Spaces
The Duel wheel is based on the star count of both players. If the sum of both players' coins is >=1000, the "All your coins" option is replaced with "Half your coins."
There are 12 possible minigames that can be played on a Duel space.
Bowser Spaces
Each of the 4 events has a base chance of occurring but will be silently changed to a different event if certain conditions aren't met.
Items
Shop Mechanics
Warp Dice Block
The Warp Dice Block can choose any blue or red space to warp the player.
Hexes
Star Spaces
Wiggler's Garden, Toadette's Music Room, and Bowser's Pinball Machine all use the same Star Space generator as Mario Party 7 (cycle through all possible star spaces, skip if a player is on it when chosen). Kamek's Library doesn't use star space cycling at all.
Wiggler's Garden
Three Tulips
The tulips have a practically equal chance of having 30, 10, or 1 coin. There is a very slight bias towards the leftmost tulip having higher coin amounts.
Bank Bulb
The reward is based on the total X movement of the stylus. Every 320 pixels of horizontal motion = 1 coin. Letting go resets the counter for the current coin to 0.
Piranha Plant
The chance for the Piranha Plant's fireball to fail is based on the player's current placing:
(The constants used are actually 10, 20, 30, and 50, but the game compares a random integer using the > operator, and random integers start at 0, so there is an off-by-one error in the chances.)
Toadette's Music Room
Hammer Bro
Hammer Bro can warp the player to any random red or blue space.
Piano Bonus
There are 3 possible songs. Which song is given is random, with chances based on placing -- higher places get harder songs more often. The reward depends on the song played and goes down by 1 coin for every wrong note. However, if you make too many mistakes (depending on the song), you won't get any coins. Time doesn't matter as long as the song is finished within the time limit.
(Once again, the odd numbers for the probabilities are not intentional)
DK's Stone Statue
Dry Bones
60% chance to get sent to the start, 40% chance to get sent to right before the Star Splurge Space.
Colored Vines
34% Double Dice Set, 33% Triple Dice Set, 33% Halfway Dice Block.
Kamek's Library
Kamek
A 10% chance to use Spell 88 (swaps everyone around), otherwise Spell 8 (swaps with just 1 player).
Crystal Ball
Bowser's Pinball Machine
Coin Roulette
The target value is chosen randomly from 1-6, with each value having practically equal probability. The wheel can be timed.
Wheel of Wonder
The wheel can be timed. The 5x wedge has roughly a 6-frame window (at 60FPS) to hit.
Pinball Plunger
The chance to go to the Star Zone depends on placing.
Minigames
Get the Lead Out
Score is 0.3 inches (centimeters outside the US) times the number of A presses. The speedometer is purely aesthetic.
Fast Food Frenzy
Once the solo player places an item, they must wait 40 frames (2/3 of a second) before placing the next. Each item also has an individual cooldown:
You are encouraged to reply with questions as well as your own findings! Everything known so far will be added to the OP.
Spaces (all boards)
Duel Spaces
The Duel wheel is based on the star count of both players. If the sum of both players' coins is >=1000, the "All your coins" option is replaced with "Half your coins."
1. 10 coins / 20 coins / 20 coins / Half your coins / All your coins
2. 20 coins / 20 coins / Half your coins / All your coins / 1 Star
3. 20 coins / Half your coins / All your coins / 1 Star / 1 Star
4. 10 coins / 1 Star / 1 Star / 2 Stars / 2 Stars
5. 1 Star / 1 Star / 1 Star / 2 Stars / 2 Stars
2. 20 coins / 20 coins / Half your coins / All your coins / 1 Star
3. 20 coins / Half your coins / All your coins / 1 Star / 1 Star
4. 10 coins / 1 Star / 1 Star / 2 Stars / 2 Stars
5. 1 Star / 1 Star / 1 Star / 2 Stars / 2 Stars
| Wheel | 1 | 2 | 3 | 4 | 5 |
|---|---|---|---|---|---|
| Both players have >=2 Stars | - | 30% | - | 60% | 10% |
| Exactly one player has >=2 Stars | - | 50% | - | 40% | 10% |
| At least one player has 1 Star, neither has 2 | - | 30% | 70% | - | - |
| Neither player has any Stars | 100% | - | - | - | - |
There are 12 possible minigames that can be played on a Duel space.
Goomba Wrangler
Study Fall
Soccer Survival
Get the Lead Out
Trash Landing
Cheep Cheep Chance
Whomp-a-thon
Crater Crawl
Boogie Beam
Dust Buddies
Cyber Scamper
Soap Surfers
Study Fall
Soccer Survival
Get the Lead Out
Trash Landing
Cheep Cheep Chance
Whomp-a-thon
Crater Crawl
Boogie Beam
Dust Buddies
Cyber Scamper
Soap Surfers
Bowser Spaces
Each of the 4 events has a base chance of occurring but will be silently changed to a different event if certain conditions aren't met.
| Event | Chance | Note |
|---|---|---|
| Gimme Equality | 10% (100% if the player has 0 coins) | Becomes Gimme Charity if the sum of all players' coins is less than 4 |
| Gimme Charity | 20% | Becomes Gimme Stars if the player has less than 3 coins |
| Gimme Stars | 30% | Becomes Gimme Coins if the player has 0 stars |
| Gimme Coins | 40% |
Items
Shop Mechanics
Games are divided into 2 or 3 "phases" depending on how long the game is:
The items available from the shop vary based on the phase of the game and the player's placing. Items with
are guaranteed to appear; items with 
are randomized, and each has an equal chance to fill the remaining slots.
| Game length | Phase 1 | Phase 2 | Phase 3 |
|---|---|---|---|
| 10 | 1-5 | 6-10 | - |
| 15 | 1-5 | 6-15 | - |
| 20 | 1-6 | 7-13 | 14-20 |
| 25 | 1-8 | 9-16 | 17-25 |
| 30 | 1-8 | 9-25 | 26-30 |
The items available from the shop vary based on the phase of the game and the player's placing. Items with
are guaranteed to appear; items with are randomized, and each has an equal chance to fill the remaining slots.| Item | Phase 1 | Phase 2 (1st-2nd place) | Phase 2 (3rd-4th place) | Phase 3 (1st-2nd place) | Phase 4 (3rd-4th place) |
|---|---|---|---|---|---|
| Double Dice Set | | | | | |
| Triple Dice Set | | | | | |
| Halfway Dice Block | | | | ||
| Warp Dice Block | | | | | |
| Snag Bag | | | | | |
| Star Pipe | | | | | |
| Block Detector | | ||||
| Grab Bag | | |
Warp Dice Block
The Warp Dice Block can choose any blue or red space to warp the player.
Hexes
First turn only
Subsequent turns
| Item | Chance |
|---|---|
| Coin Swap Hex | 5% |
| Space Swap Hex | 15% |
| 10-Coin Hex | 80% |
| Item | Chance |
|---|---|
| 10-Coin Hex | 10% |
| 20-Coin Hex | 20% |
| Coin Swap Hex | 10% |
| 1-Star Hex | 30% |
| 2-Star Hex | 10% |
| Space Swap Hex | 3% |
| Star Block | 7% |
| Coin Block | 10% |
Star Spaces
Wiggler's Garden, Toadette's Music Room, and Bowser's Pinball Machine all use the same Star Space generator as Mario Party 7 (cycle through all possible star spaces, skip if a player is on it when chosen). Kamek's Library doesn't use star space cycling at all.
Wiggler's Garden
Three Tulips
The tulips have a practically equal chance of having 30, 10, or 1 coin. There is a very slight bias towards the leftmost tulip having higher coin amounts.
Bank Bulb
The reward is based on the total X movement of the stylus. Every 320 pixels of horizontal motion = 1 coin. Letting go resets the counter for the current coin to 0.
Piranha Plant
The chance for the Piranha Plant's fireball to fail is based on the player's current placing:
| Place | Chance to fail |
|---|---|
| 1st | 11% |
| 2nd | 21% |
| 3rd | 31% |
| 4th | 51% |
Toadette's Music Room
Hammer Bro
Hammer Bro can warp the player to any random red or blue space.
Piano Bonus
There are 3 possible songs. Which song is given is random, with chances based on placing -- higher places get harder songs more often. The reward depends on the song played and goes down by 1 coin for every wrong note. However, if you make too many mistakes (depending on the song), you won't get any coins. Time doesn't matter as long as the song is finished within the time limit.
| Song | Base Reward | Max Mistakes | 1st Place | 2nd Place | 3rd Place | 4th Place |
|---|---|---|---|---|---|---|
| CAGEDBC' | 20 | ? | 61% | 41% | - | - |
| BAGDE | 17 | 5 | 39% | 59% | 49% | 29% |
| C'FG | 15 | 3 | - | - | 51% | 71% |
DK's Stone Statue
Dry Bones
60% chance to get sent to the start, 40% chance to get sent to right before the Star Splurge Space.
Colored Vines
34% Double Dice Set, 33% Triple Dice Set, 33% Halfway Dice Block.
Kamek's Library
Kamek
A 10% chance to use Spell 88 (swaps everyone around), otherwise Spell 8 (swaps with just 1 player).
Crystal Ball
| Reward | Probability |
|---|---|
| 30 coins | 45% |
| 1 Star | 10% |
| Star Pipe (if inventory is full, becomes 30 coins) | 45% |
Bowser's Pinball Machine
Coin Roulette
The target value is chosen randomly from 1-6, with each value having practically equal probability. The wheel can be timed.
Wheel of Wonder
The wheel can be timed. The 5x wedge has roughly a 6-frame window (at 60FPS) to hit.
Pinball Plunger
The chance to go to the Star Zone depends on placing.
| Placing | Chance to go to Star Zone |
|---|---|
| 1st | 10% |
| 2nd | 20% |
| 3rd | 25% |
| 4th | 30% |
Minigames
Get the Lead Out
Score is 0.3 inches (centimeters outside the US) times the number of A presses. The speedometer is purely aesthetic.
Fast Food Frenzy
Once the solo player places an item, they must wait 40 frames (2/3 of a second) before placing the next. Each item also has an individual cooldown:
| Item | Cooldown (frames) | Cooldown (cycles of 40 frames) |
|---|---|---|
| Shake | 160 | 4 |
| Burger | 220 | 5.5 |
| Pancakes | 130 | 3.25 |
| Hot Dog | 40 | 1 |
| Fries | 100 | 2.5 |
| Ice Cream | 40 | 1 |
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