Weapon Drops-
When a player dies in co-op, a teammate may elect to switch out their weapon with one of the dead player's for the duration of the level. The dead player retains their weapon set, however, and players can choose to switch their weapons back at any time

This would encourage players to try out new styles of weapons--a preview run, if you will.

Key Guardian enemies, randomly boosted enemies-
Monsters may occasionally be seen carrying a key or statue instead of the aforementioned object just lying there for the player's taking. They would appear either larger, scarier, or both, and would drop the item upon death.

Monsters may occasionally have Speed, Attack, or Defense boosts. These monsters would drop slightly more crowns or heat than average, due to being harder to kill, plus a 100% chance of dropping their respective Boost pickup.