Blat

As a melee class it's a bit of a PITA to be up against it, if not only because of the sheer amount of damage those other blobs do.
Since the "main" blob is faster, all I had to do was to get out of range of the other blobs and still in range of the main one, by backpedaling a bit.
So, no slowing on the "boss". After that, it was a piece of cake.

Kite it and kill only the main slime, the slimes from split move slowly :)

First boss that makes a tank happy. You can just tank all the oozes for vengance and pew the boss hard and fast. Especially paladins and warriors (block tanks) who can greatly reduce the damage of copies by maximizing block up time.

I kited at first thinking the copies were an insta death mechanic like most other bosses. They really are just ordinary copies and not threatening to just tank them. If you are a tank don't be afraid to just build vengeance. :)