Warhammer 40,000: Battlesector

Can be done in a hot seat multiplayer game with a 2nd controller. To make it easy set up a new army list with just the lieutenant in it (on the main lobby screen under army management, press Y to set up)and sign in both controllers as the same profile on the setup screen. Then just beat him with army of your choice.

Update: as per stealth finger advice below, this has to be a direct attack not letting him die of poison damage, thanks