Are there any items that Decrese your speed,making you fastEr in a trick room
In Gen 8, an item called Room Service was introduced. It only activates in Trick Room and lowers the holder's Speed by one stage. Other than this, the Power items, Macho Brace, and Iron Ball are the only other items that reduce Speed. You can reduce Speed EVs with the Tamato Berry, but this isn't the in-battle state.
The Power Items, The Macho brace, and The Iron ball are the Items that Decrease speed.
Note: The Lagging tail does NOT decrease the speed stat it makes you move last which would still be last in T-room.