Steelrising

This boss fight is hilariously easy compared to the other 3 you will have fought beforehand, the Treasurer is all looks and no concept of personal space.

From the beginning of the fight the Treasurer wields a ginormous key that it will swing around itself to try and hit you if you're in reach or slam the key onto the ground where you're standing. The Treasurer will also use said ginormous key to insert into his chest and release one of 3 different attacks depending on the phase.

Phase 1) If the Treasurer inserts the key into the lock in it's chest it'll release 3 small flying bombs that will fly towards you and explode inflicting a small amount of Fulmination build-up.
Aside from that you just need to dodge/block/parry the attacks from it's key.

Phase 2) - Now the Treasurer will raise the key in the air and summon lightning to strike in a circle around him and activate lightning on the key. This is easy enough to back away from as the ground around the Treasurer will light up blue before the lightning appears. Now you'll need to be extra careful and dodge/block/parry at the right moment or you will end up getting the fulmination build-up which'll make you take increased damage till it runs out or you take an elixir.
- While the Treasurer's key is infused with lightning it'll do big overhead slams onto the ground which'll want to avoid.
- Alongside this the Treasurer will leap into the air and try slam it's butt onto your face, I think it's safe to say that if you don't want to be teabagged by the Treasurer you should definitely move out of the way rather quickly. Plus side to this attack is that the Treasurer leaves his backside vulnerable for a little bit of payback while he recovers from what may be a bit of a sore butt.

Phase 3) Now the Treasurer is getting a little fed up with his (hopefully) unsuccessful teabags and has decided to take his attack one step further. The Treasurer will now insert the key in his chest and charge up before leaping into the air and attempting to bodyslam you, inflicting serious damage if you don't move out of the way in time.
- When the Treasurer isn't trying to bodyslam you, it'll do a weird little wobble walk towards Aegis before slamming the key (permanently infused with lightning) down in front of him, releasing a huge trail of lightning in a straight line. The attack will be enough to kill some players if you get caught in the middle of it, so best to put on your dancing shoes and prepare to sidestep away when the Treasurer starts his wobble walk.
- The Treasurer will also do a big vertical swing with the key in front of him, so to avoid a whopping headache I suggest backing away or dodging behind him to get a few hits in.

To speed this fight up immensely you can make use of grenades, namely explosive, frost and flame grenades which the Treasurer is highly weak to.
- It takes 4-5 frost grenades to fully freeze The Treasurer, and it'll give you plenty of time to do enough damage to take at least 1-2 health bar chunks away.
- It takes 5 flame grenades to set the Treasurer on fire. I highly recommend doing this as this will make the Treasurer lose alot of health regardless of how much you're attacking it (roughly 2 health chunks).
- Explosive grenades take a couple hundred health per grenade and are just genuinely a great thing to throw when you're keeping your distance waiting for an opening.

Otherwise have fun and go hard, and enjoy what is a nice relaxing fight compared to the other Titan bosses.
Also, try to be right by the Treasurer's body for the killing blow so you can pick up it's loot immediately before the cutscene starts. After talking to your new comrade you'll be fast travelled with them to Luxembourg (if you chose the Cordeliers Convent dialogue option at the end of the conversation). The Treasurer's body might disappear and therefore leave you without a VERY PRECIOUS item needed for weapon upgrades!