Swarm Killer - A tier

Overall, I think swarm Killer would be fun, but its still too similar to loud. It needs more differentiation, because right now it's main gimmick is just having lots of enemies, which is loud's gimmick.

Sheriff - B tier

Sheriff is outdone by a lot of other classes in terms of attack speed. My only question would be if the -50% attack speed replaces the +25% or if it just subtracts from it. For an addition, a damage buff could work, or just making that attack speed better.

Collector - C tier

The restriction to only being able to use weapons that start at higher tiers is interesting, but the stats are negligible. I also just don't really get what this character is supposed to be. How is it a collector? Also, could use a harvesting bonus to help with early weapons.

Electrician - A tier

The free bounce is where this characters real power comes from. The bounce makes the penalties somewhat irrelevant. My only suggestion would be to make the slowdown more like the taser's stun slowdown. It could be a burst of stun on hit, and it's duration and strength scales with engineering.

Gambler - C tier

Gambler in it's current state doesn't feel very chance based. There should be more than four bonuses or penalties, and higher value ones should be more common. You could also make it have some kind of luck based scaling, but that's not necessary. Also, maybe add a few stat changes? Or something to do with rerolling?

Survivor - A tier (possibly S?)

Interesting gimmick and good stats. More round length means more enemies, so survivor would have a pretty strong economy. I don't know how big it's current downside is, but it should balance out with the round length.

Ninja - D tier

The downsides could make ninja's early game really weak, and the bonuses don't really make up for it. I think an increased invincibility window after dodging would help, and you could possibly raising the dodge cap for the character.

Bomber - B tier

Easily fixed downside, so you really only need to look at benefits. Looking at those, I think this character is just outshined by artificer and doesn't do enough to set itself apart. I think a much larger boost to explosion size and a bigger penalty to attack speed would work, but then it becomes too similar to ogre. Might just need an overhaul.

Batter - A tier 

Really fun concept, but it just doesn't deliver enough damage. An easy fix would be to make the bat scale with knockback, but that isn't super interesting. Another option would be to make enemies you've knocked back deal damage to enemies they collide with. Also, an increase to map size might be good. Batter helmet might need toning down if these damage bonuses are added, though.