FractalFusion, thank you for explain.
My summary about instant kill trick.
The two things are necessary for instant kill.
1) Set R.Mine close to the boss.
2) Equip Counter Attacker and it's active.
Only the fight with Tengu Man allow for control in boss room. If I try same way to other bosses, character stuck in bottom corner, and it become impossible to continue playing game. Here is its screenshot. http://twitpic.com/3w0iqx
Burner Man room is similar to Tengu Man's, but acus and bridge obstruct it. Instant kill Wily is realized by other way, using two weapons at the same time, normal shot and R.Mine.