The Beware Squares: Any piece that lands on it gets captured. They start on d4, d5, e4 and e5.
Invent the new worst/most useless chess piece ever!
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The yawning pawns: replaces all 8 pawns and cannot move or get captured. only allows knights to move past .
The Interweb - begins a debate between the two players over trivial issue once it is moved (moves like a king and starts in the place of the pawns). Whoever 'wins' the debate determines the outcome of desired move.
The nothing; Has no art, and you cannot see it. Starts on d4 and cannot be moved. Any piece that ends turn adjacent to The nothing becomes a nothing
The plug. It covers the whole board and prevents anyone from playing
The Barock. It has no effect to your opponent but blocks your pieces from moving through or occupying the square.
the giraffe can only move 9 squares in any direction and then 1 square (like a knight) XD
the valley
any piece that is on it falls and disappears, covers 2x4 area
starts on center of board
both players can move it, but when moved, the player who moved it loses the next 2 turns
The tiny pawn.
Moves like a normal pawn, but cannot capture because it is too small. Also, it can be squashed by any other piece. It really is useless.
May 3, 2017
0
#392
The customs officer. As long as he's on the board, you have to give all your social media passwords to your opponent whenever any of your pieces would enter or cross the 5th rank. Terrible piece in my opinion. Let's never use it.
The toll booth. Same concept as @evert823's idea, but you have to give up that piece instead of sharing your social media passwords XD. Or, alternativly, you could pay a toll fee of 2 gold bars, or $650000.
May 3, 2017
0
#394
The drunken king. The piece is on a base, lying on its side. It is put on the board only when resigning.
XD LOL brilliant idea! 
The karate guy: Move it, and he'll karate you.
the betrayer
the opponent chooses a pawn from the other side and marks it on the bottom. If a pawn promotes and is the betrayer pawn, the promoted piece becomes a piece of the enemy side
The 2q. if you capture it 5 more appear on the board, none contribute anything, they just take up space.
May 14, 2017
0
#399
the mirror:
it doubles all the pieces every move, nothing will change but the amount of pieces you have to move every move.
p.e.:
1. e4 [1 Pawn] e5 [2 Pawns to move] 2. Nf3 [4 Knights to move] Nf6 [8 Knights.....
@Bonsai .. this is strange
The "Defector" - before the game begins, each player chooses three of the eight pawns of his or her opponent and marks them with a dot on the bottom. The pawns are randomly placed by the other player into the standard starting position, together with the other pieces. The game is played normally, but with the exception that when a pawn marked with a dot (a 'defector') achieves promotion, that pawn instead turns into a queen serving the opponent. A captured pawn may NOT be checked to see if it was a defecting agent or not; this can only be done upon promotion.