Warhammer 40,000: Mechanicus

Keep doing missions for Captrix (fifth down) and you’ll get one called “The Corrupted King”. Cheevo will pop and mission will end as soon you defeat Ubjao. It has no armor and around 20hp to start with. Every time you defeat an add-on creature Ubjao gains 4hp. Each turn it calls for more creatures to show up. I rushed Ubjao spending CP and avoiding the add-ons to defeat it quickly up close.