Sufficient mating material, less a king? As an extension to this question about can a rook and knight without a king stalemate a opposing king, and the traditional minimum-mating-material question, I had a puzzle question:

What are the minimum combinations of material (without a king) required to forcibly mate an opposing king? 


R + R/Q is clearly sufficient
R + N + N/B maybe, as an extension from the above stalemate question


On the other hand, there are some sets that fail without a king:


B(w) + B(b) (but 3 bishops should work, so long as one is on a different color)
Assuming opponent has no pieces:


4 or more knights
4 or more bishops, at least 2 per side
At least 2 pawns, but it also depends on where the pawns are
2 or more major pieces
Queen and a minor piece
Rook and 2 minor pieces
4 minor pieces
Pawn+Minor pieces/2 Minor Pieces(depending on where the pawn is or a major piece


If opponent have pieces:


Queen(maybe rook)+Minor Piece vs 1 pawn
Queen(maybe rook)+2 pawns vs Rook+Bishop+Pawn
Q+R vs Rook and bishop or 2 minor pieces(for most positions)