I have some ideas. First, I have the Ugly Cluckling, which is an Imp wearing a chicken suit, and he has Feather Blasters which are rapid-fire and go through multiple enemies. When he calls in his Mech, it lands on top of it, like S.H.R.Imp, and when he ejects from it, he gets shot out from the Mech's bottom, like he is an egg. The Mech has two large robotic chicken legs and a control station for the Imp in the middle.. The Mech has explosive Yolk Impactors which can leave Plants unable to use their abilities. The Mech has two abilities; 1) Whirlwind, which makes the Mech spin its legs like a tornado, which suck in and deal damage to Plants, and 2) Cluck Jump, which makes the Mech jump in the air and hover for a few seconds before coming back down and dealing damage to Plants near it.
Another idea is the Winter Giggler, which is an Imp dressed like a snowman, and is the ice variant of the Imp. His Mech resembles a giant snowman whose two abilities are; 1) Snowball Flurry, which makes the Mech shoot out rapid-fire damaging snowballs, and 2) Frost Wave, which makes the Mech slam the ground and create a large icy wave, which instantly freezes nearby Plants.
A third idea is the Lil' Driller. He is a miner-themed Imp who has slow firing but does large damage with his Drill Diggers. His Mech moves around on one giant drill on its bottom, and has two long robotic arms, and the Mech shoots one large bomb at a time which explodes after a few seconds using his Big Bomb Blaster. His two unique abilities are; 1) Dirty Dig, which allows the Mech to drill and move underground, and when it is below a Plant it can emerge and deal heavy damage to the Plant, and 2) Pickaxe Toss, which makes the Mech throw pickaxes that act like boomerangs, which come back to the Mech after a short period of time, dealing double damage to Plants.