Traps

Traps are obstacles in dungeons. They will appear in any square on any floor of a dungeon.

Chestnut
Drops Chestnuts on whoever steps on it for 10 points of damage.

Spin
Spins the Pokemon around and confuses it.

Explosion
Creates an explosion that spans 24 squares around it. Damages anyone caught in it, and destroys all walls and items.

Gust
Throws the Pokemon across the room until it hits a wall.

Mud
Decreases one random stat by 1.

Pitfall
Deals 5 damage to a Pokemon and drops them to the next floor. Only appears in dungeons with descending floors.

Poison
Inflicts poison status.

Pokemon
Causes the items in the room to turn into Pokemon. No effect if there are no items.

PP Zero
Drops a random move's PP to 0.

Seal
Seals a random move. The Pokemon can't use this move until it leaves the floor.

Self Destruct
Creates an explosion that spans 8 squares around it. Damages anyone caught in it, and destroys all walls and items.

Slumber
Inflicts sleep status.

Slow
Decreases speed by 1.

Sticky
Causes a item to become sticky and unusable.

Grimy
May cause food items to be come grimy food.

Spiked
Deals 20 damage with piercing spikes.

Summon
Causes Pokemon to appear.

Warp
Warps the Pokemon to a random place on the floor.

Other traps were introduced in Pokemon Mystery Dungeon 2:

Stealth Rock
Deals 1/8 of the Pokemon's max HP

Toxic Spikes
Deals 10 damage and inflicts poison status.

Trip
Makes the Pokemon drop it's held item.