I think the buff drops were a great idea, but they need a bit of tweaking.

I think that the buffs that drop from a monster should reflect the monster itself. For example, an Alpha Wolver (which can buff his attack power) should have a higher chance of dropping an attack buff. Wolvers, since they can also dash, should also have an increased chance of dropping speed buffs (and possibly Devilites, as they can dodge bullets well). Maybe Trojans and Deadnaughts, and tier 3 zombies (since they all carry shields) should have an increased chance of dropping defense buffs.

It'd also be interesting if creatures dropped status resistance buffs, e.g. a toxigel dropping a poison resist buff, or a rocket puppy dropping a fire resist buff. You might also want them to drop status damage buffs, which would have a chance to inflict that status effect on an enemy you hit. Obviously, these wouldn't reflect the monster that dropped them, cause it would make sense that that you wouldn't want to inflict a quicksilver with shock, or anything like that. I hope you guys like my idea, if you have any further suggestions, post them below. I'd like to hear your ideas as well!