Commander Yammark: Ray Arrow
Ground Scaravich: Yammark
Blaze Hentnix: Ground Dash
Blizzard Wolfang: Magma Blade
Rainy Turtoid: Ice Burst
Metal Shark Player: Meteor Raiin
Shield Shelden: Metal Anchor
Infinity Mijinion: Guard Shell
Dynamo: Meteor Rain
High Max: Magma Blade
Gate Boss 1: Metal Anchor
High Max: Magma Blade
Gate: Invinsible Dash or Shadow Armor Giga Attack
Sigma 1: Metal Anchor
Sigma 2: Ground Dash

To easily defeat any Boss or mini-Boss, enable the 'X's Ultimate Armor' code. Get to the Boss and use Giga Attack two or three times. Also, use this strategy to defeat High Max. Hit him with a charge shot while he is flashing, then immediately use Giga Attack on him. Do this three or four times to kill him.