A note on Wood Man:
Metal Blades do work. However, Crash Bombs which hit his shield immediately explode, and the explosions will go through the shield and hurt him. This is the cheap way to beat him.
If you really want to be 1337, though, charge up the Atomic Fire. Uncharged (Level 1) shots and semi-charged (Level 2) shots do nothing, but a fully charged shot (Level 3) is an instant kill, doing the full 28 points of damage in one hit.
Upon further investigation, this only works as an instant-kill on the US version's "normal" mode. This mode never existed in the other versions. In the US game's "difficult" mode and all other versions (including the Mega Man Anniversary Collection's Normal mode) a fully-charged Atomic Fire only does 14 points of damage, dropping Wood Man's energy by half. MMAC's Easy mode corresponds to the US game's Normal mode, so the instant-kill still works there.