Here's some mechanics I'd like to see:
A gun that jumps to hit two enemies, similar to those quills, at the cost of doing around 55%-65% damage.
A gun that, on hitting an enemy, queues that enemy to take damage as soon as a different enemy is hit. Should deal a bit of extra damage to reward the complicated aiming, maybe 10%?
A gun that picks up any loot it shoots over. Attack pattern should be at least similar to a Pulsar with a clip of one, so it can pick up a whole lump of treasure without being spam-able.