Gunkers are easily identified by the white/blue colour, the red gas canisters lodged into their backs, and their ice projectiles.
I completed this challenge by doing the mission "Getting the Band Back Together
". Also ensure that you have the "Second Amendment" amp
enabled for the One-Handed Dragon.
While you are towing Wendy's boat with the harpoons (near the beginning of the mission), your character will yell "Gunkers!" as 3-4 spawn. You may need to kill 2 before another 2 spawn.
When you are certain no more gunkers will spawn, let the OD kill you, and you will respawn... for your character to shout "Gunkers!" again, and the 3-4 gunkers will respawn. Make sure to kill yourself before Wendy's boat reaches the dock!
Rinse and repeat; it shouldn't take more than 20 minutes.Brief video guide: