Since this thread already has been going on with suggestions for guns and bombs, I might as well start suggestions for new pickups (like vials n' stuff for those who dunno).
Here's a suggestion from myself, make some sort of pickup that casts out a small circle of AoE. Within the radius, it will lower the stats of monsters caught inside. No damage, only lowered stats. There can be a couple variants of stats lowering: attack, defense, movement speed or attack speed.
Leave any suggestions about your own pickups or what you think about my pickup!
Something that can give benefit to teammates like a little AoE hp regen? Not to be as powerful as health capsules since it can heal teammates. maybe 1-3hp units depending on tiers.
Or a teammate revive thing? Supposed to be really rare that you can only get 1-2 in a full arcade run...