Magnet Bomber: [link]
Golem Bomber: [link]
Pretty Bomber: [link]
Brain Bomber: [link]

*****

Plasma Bomber is the leader of the Bad Bombers and as such is a well rounded opponent, equipped with throwing and kicking abilities, as well as bombs with an above average blast radius. He's fast too, and pilots an awesome skull-headed monster machine which turns out to be a giant eyeball in disguise(?)
Right before his demise Plasma Bomber extends his hand to shake - assumedly as some sort of ruse - but is zapped by his malfunctioning machine. Then he reappears in SBM3 and pilots a ridiculous princess doll thing, as the machines were themed on the world you were visiting, rather than the bomber you were fighting.