A Bazooka that shoots Rocket Puppy rockets. It could be a craftable gun, it could be a promo item. Maybe both and have the craftable version shoot straight rockets with the promo item shooting homing rockets to make it more pay to win. If its craftable it would be good to have it require a new material that can only drop from Rocket Puppies so that players can't just straight up craft it but actually have to go hunting in the clockworks for them.

Rockets function almost exactly like rocket puppy rockets: they explode on impact and if the user stands too close to the explosion then they take the explosion damage. The only difference is there is no friendly fire on allies.
Fire rate is slow and knocks the user over like the old magnus charge cause that is cute.

Maybe it would be fun to have it benefit from both Gun and Bomb bonuses. So that a Shadowsun armor set boosts its damage but a Mad Bomber set does too. Or give it no regular attack, only charge attacks which will automatically slow down its fire rate and make it classified as a pure bomb.

Or maybe make it just a pick up item that you can get in levels and give it 5 ammo.

Giving it a mechanic that makes the projectile follow your mouse cursor until it hits an enemy and explode would be cool, but only really compatible with WASD controls I suppose. But it would be cool as heck