What are the quckest helpmates delivered by the rook, knight, bishop, and pawn? What are the quickest helpmates, which is where both sides help administer checkmate to one side,  delivered by the rook, knight, bishop, and pawn? The said piece has to deliver the checkmate on the final move.
Here's what I came up with.

Bishop took me 3 moves:

[FEN "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1"]
1.e4 f5 2.Be2 g5 3.Bh5#  *


Knight took me 3 moves as Black:

[FEN "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1"]
1.e4 Nc6 2.Ne2 Nd4 3.g3 Nf3#  *


Pawn took me 5 moves:

[FEN "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1"]
1.e4 Na6 2.Bc4 Nb4 3.e5 Na6 4.e6 Nc5 5.exf7#  *


Rook initially took me 6 moves, with 1.h4 f5 2.Rh3 f4 3.d4 f3 4.Rxf3 g6 5.Bh6 Nc6 6.Rxf8#. But I found a quicker way to checkmate with a rook - promote to one! This results in a checkmate in 5:

[FEN "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1"]
1. g4 Nh6 2. g5 g6 3. gxh6 Bg7 4. hxg7 Na6 5. gxh8=R#