Warhammer 40k: Dawn of War 2
It's also possible, albeit incredibly drawn-out, to use "mega unit" on the boss to make them killable. It takes a really really really really really long time to kill them, though. Like, really long.
If u accidently weaken it, u'll need to mega the boss hp to normally 999999, taking u around 10 min non-stop heavy fire to make it drop to a certain level entering the tank....