From Sonic Retro
Triangle Dive (トライアングルダイブ Toraiangurudaibu) is a move shared by both Team Sonic and Team Dark in Sonic Heroes. Activated as either Knuckles or E-123 Omega by holding (GCN & Xbox)/ (PS2) in the middle of a jump, Triangle Dive sees the entire team arrange themselves in midair like skydivers, power gliding to slow their descent.
The move enables the characters to fall slowly; or, more usefully, catch an updraft and ascend. The technique first sees a use in Ocean Palace, riding the output of the floor-mounted giant fans to glide up the sheer ruin walls.