You get... WARP BUSTER

---------------------------------------------------------------------------
You get this weapon from Warp Man ([link]). Megaman shoots out a purplish buster shot. In-game, If it hits small enemies (like Mets), the enemies are instantly sent off-screen. On larger enemies (like Big Eyes), they are flung a short distance away, while being dealt with a small amount of collision damage with the ground. For lightweight enemies (HINT HINT), they are flung right into the nearest wall, causing a lot of collision damage.
---------------------------------------------------------------------------
As such, this is Coat Man's ([link]) weakness.
Sprites used from Sprites' Inc
Concept from my evil mind...