How can i beat this boss?

[SandwichPower]

I went into the temporal rift and got to the chronolith twin. I beat the clone, but the twin seems actually impossible to kill. I can use every single attack i have and it will deal barely any or no damage whatsoever. The lowest I've gotten him is 91%, which he then healed back by putting up shields, pushing me away, or making me blink nonstop. When I hover over his health bar when dealing several auto attacks, he doesnt lose any health. And i do mean any. I've beat him before and don't remember having this kind of trouble. I'm playing as a skeleton bulwark and I'm level 21 if that helps.

[Coldbringer]

Open the combat log by pressing the H key and have a look at the messages. That should give you some info as to what is happening.

I haven't looked at their skill list in a while (you can click on and inspect monsters, opening several tabs to see lots of details about them) but I know chronomancers have several powerful damage mitigating skills and an excellent shielding skill. It can be a wiser tactic to run around a corner and get cooling down skills & resources back as they chase you and don't have line of sight on you to attack. Meanwhile their shield wears off and goes on cooldown for x amount of turns.

If you have a way to remove magical effects and sustained skills that helps a lot here. Like gloves of dispersion.

[HousePet]

I'd say 21 is a bit early to be there.

I'm not sure if it can drown if it goes too far into the water, so that might be an option.
Otherwise you are going to have to be tactical with stuns and attacks.

Now checking the code, as something seems off here...
Any damage done to one is repeated on the other at a half rate, so that isn't reducing your damage.
Neither get any healing inscriptions, so that can't be a problem.
I can't see any invulnerability like code.
However it may have generated with an item that is giving it some good damage reduction or life regen.

You'll just have to examine the log carefully.

[SandwichPower]

Ok, so I realised the problem was that he spawned with 90% physical resistance and 9% all resistance. So I was dealing minimal damage to him with most of my attacks. So I swapped my mace to Stormlash and swapped my gloves with ones that had fire damage and after many turns of dealing 1% total health damage I beat him. Thanks for the help guys! I didn't even think to check the stats at first.