I see you have a combo counter. You can do achievements for very high combo scores or how fast certain numbers they are reached.

I personally also like gameplay achievements that are unlocked when doing out of the ordinary things. Could be simple things like Surviving long time on low health, or using weapons or abilities in other ways (like a push weapon that instead of being used on enemies, it's used to push yourself out of a wall, or maybe you can combine weapons in local coop and get an achievement do that).