Invaders and helpers

 

Black to move

1k6/1b3p1p/p7/3qp3/Np5Q/4BP2/PPP3rP/R4K2 b - - 1 26

Jean-Marc Degraeve vs. Laurent Guidarelli (2003)

Source Chessable The Checkmate Patterns Manual

• The black queen and bishop cooperate to invade f3
• Once invaded, a new invasion square emerges: The black rook and queen eye to f2
• But that focal point is defended by the white queen and bishop
• After 1. ... Qxf3+ 2. Bf2 the helper black rook sacrifices itself 2. ... Rg1+ and acts as a magnet to attract the white king to another square 
• White gives mate from one of the two invasion squares g2 or h1

The invasion squares are clearly dynamic, and move with the pieces