I donāt really care much about PvE, but my suggestion would only allow 2 copies of the second form. Not multiplying the awakened form with a 66% chance, which creates those absurd situations like the one shown above with over 100 copies.
This is how I deal with it in PvP:
I made the dumb mistake of killing it without void, created a nightmare horde of unkillable thalazzans. This is worse than Astra for sure.
My bad. I somehow mistook it for summoning 2 copies of itselfā¦
My idea is to remove the death immunity from the awakening form and transform into two split bodies (with death immunity) after death. The split bodies will have 35% health after resurrection, and the three skills will evolve into adversity, that is, after killing monsters, the three skills will be reborn as two heads
Or it could just split in two of its previous evolution. (bad idea right)
Today I came to know I am AI not real player 
Ah yes, Iāll leave it to the end alongside Astrajlyth, Pandora, Isoldelle, Alyce and Dameuleā¦ none of which I can kill without putting myself into a losing position unless I have the correct type of move. Maybe throw in a Shi Na, Jeanne dāArc or Risu that I canāt deal with either.
Thatās sarcasm of course and in all seriousness my tactic for facing these is literally exactly what you sayā¦ leaving them until the end. Surely you can see thatās super unhealthy as a solution for how to deal with monsters, it highlights how seriously problematic the designs are! Iām glad you havenāt done more āuntargetableā monsters because that was a horrible mechanic but unkillable / unbreakable shield / revive copies are also terrible if you donāt do them right.
Speaking very seriously and purely for the reason of feedback (without any rudeness intended towards anyone)ā¦
There is absolutely no way anyone could defend whatās happened to Thalazaar. Itās completely flawed and nothing to do with PvE vs PvP. Itās a really big blunder made by the people involved. Itās okay to mess up sometimes. The last update which made heal effects instead make the monster die was kind of funny. We just need this nonsense reverted. Imagine it doesnāt exist and go in with a fresh mind.
So letās all agree that the concept of it splitting into more hydras on death is cool. Big thumbs up to that! The speed buff, cost reduction and death immunity have all improved it quite nicely as a monster design too.
How to go about doing the hydra splittingā¦
Coltrazās idea of it coming back as 2x second form is a great one. Double energy burst still one-shots so theyāre absolutely not dead weight and you could make this 100% chance. Given the other moveset buffs, this could be enough. They could enter with either 50% or 100% HP, whichever you want.
What I would have suggested is a single split into two of the final form with 100% chance, entering with 50% HP. I think going beyond that is excessive. The monster might not be competitive in its release state but thereās no doubt itās not a threat. It will get kills if given any time to do so. Creating two more threats on death is legitimately good.
Another idea that could be cool is making the first split be 50% chance to make two final forms with 66% HP and each of those has 25% chance to make two final forms with 33% HP. This makes proper use out of the moveset doing different things at each HP threshold. So the first pair would have the high attack for energy blast and the last ones would have adverse smash ready on the first turn. Youād get up to 7 in total but youād actually get is as:
1 only (50%)
1 + 2 only (28.125%)
1 + 2 + 2 (18.75%)
1 + 2 + 4 (3.125%)
Please note these numbers are just random ones I picked. Iād recommend starting with them, then if itās not enough you could instead make it 66% and 33% chance to split. With that youād instead get the following:
1 only (33%)
1 + 2 only (30%)
1 + 2 + 2 (29.6%)
1 + 2 + 4 (7.3%)
Whatever you choose to do, I recommend leaning on the side of caution. Itās always easy to make small buff adjustments later. However, saying āthis monster was a bit weak, letās make it have 15 lives instead of 1ā is easily going to go overboard.
Lmao. This is my exact sentiment.
You can do a quick experiment; you just need a regular dice.
-Imagine youāre in the basement and chained by your foot. The only way to open that shackle is by rolling a dice, but only if you roll a 1 or 2. If you roll a 3, 4, 5, or 6, then they add another shackle that opens the same way.
-By probability, youāll most likely end up covered in chains and locked there forever unless you cheat.
-If you donāt ignore this monster until the end of the game or kill it with something to ignore its revenge, youāll end up playing that dice game.
-That resurrection ability would be absolutely broken on any monster with a decent attack.
It is not necessary to do the experiment, it was already shown that many times it tends to an infinite loop.
It seems a good idea, which would also be given a change to the second way, but nothing that can make it the final form other time
Eh.. maybe it would lose some appeal by evocking immediately its second form?
Another idea could be: give Thalazaar 100% chance to evoke two Thalazaars, however the new copies will have their abilities replaced with just the ability to evoke, for 50% chance this time, their second form. (If we want to be petty the second form could also have 25% chance to evoke its previous evolution 
) This way the splitting idea would be retained, but it will be the whole species to be dangerous rather than the single mythic by itself.
Iām not playing PvP, but Iāve encountered a few teams with Thalazaar on the Garcia event and its just broken.
Just cap the limit to guaranteed 2 2nd form of the myth with a 100% chance or 66% for 2 awakened clone .
This passive then changes (after death) to some kind of entrance bonus like astra to help with sweeping from the revsā¦ and not remain a dw.
Probably just have a charge at entrance when they revive after death.
Just tested battling Thalazaar for the first time. This monster needs a hot fix. Literally the most ridiculous buff ever. Itās literally impossible to defeat it with the majority of monsters in the game. It will just keep multiplying indefinitely.
You litrely have an alyce, who can kill it, why in the world would you target it with other monsters when you have a void option?
secondly, ignore revenge?
If a monster dies when killing another monster the revenge is ignored, the bomb move is therfor psudo void
Waiting 150 seconds praying that they don't kill her is stupid.
I was sure someone would say this. You completely missed the point. It doesnāt really matter either in this case since I would have lost the fight anyway (the Thalazaars would have blasted through ALYCEās HG eventually).
Yes, there are a few monsters with void or bombs etc that can stop it before it multiplies. However, 90+% of monsters in this game donāt have these moves. You canāt defeat it with payback or death revenge either because of death immunity. You canāt defeat it with mirror revenge either since you will just be stuck in a loop of Thalazaars.
Here I wanted to test how his 66% chance activates if I try to kill it normally. And that way itās just impossible. This monster is completely broken.