Warframe: Atlas and Inaros

Powerful, sturdy, and slow. That's what these two have in common.

Atlas

Supposedly once one-punched a doomsday asteroid into dust, you can get his blueprints from the Jordas Precept quest and subsequent golem assassination quests. Do note that without a super strong archgun killing the HP sponge golem is going to take a long while. I made sure to get a Velocitus from the syndicates to make this go faster.

The Atlas is pretty sturdy unless he is punching, which for some reason takes him from sturdy to invulnerable. As long as he isn't jumping he cannot be knocked down and his other abilities include turning things into stone (and then punching them for more damage), making a rock wall which he can then push into a boulder and summoning stone elementals because... why not? Ultimately you'll probably want to be boxing the entire time though, which lowers his utility in many missions for me except one: he is the perfect opponent for the melee focused teleporting bastard Tyl Regor on Uranus, who you will need to grind if you want an Equinox warframe.

Inaros

You can get this Egyptian themed vampire from the Sands of Inaros quest, which is a bit tough especially towards the end as you need to fight an Inaros with a toxic bow. Easy peasy for a patient and invis Loki though. Your reward is a terribly hungry monster who almost literally cannot die. Even when he is downed, he doesn't go into bleedout pistol mode like the others - he gets into a sarcophagus that does TRUE damage (no resistance against it) and should he kill two targets (friend or foe) he returns to the fight fully rejuvenated.

His main abilities also focus on taking health from his enemies for himself, and using devour lets you eat something (slowly) while completely invulnerable, which is spammable if you have the energy to do so. Finishing an enemy this way also turns it into your minion which is neat. I felt this did make his gameplay kinda slow though - fight through an area, eat eat eat. Repeat. Who knew being immortal wouldn't be much fun? If you like blocking nukes with your face and then just laughing insanely because even that didn't kill you - this might be the warframe for you.