I'm really confused about this fight and I have read to guides on him. What I don't understand are the buffs on the left side of my screen:

Celestial fire
Swarmed
ensnaring roots
(there was one other with a yellow symbol)

What am I supposed to block/fight through?

Rather than wasting turns to block the attack (which I don't know possible or not) I'd suggest to kill the 2 ferrikkis as soon as possible because they have buff that can double the damage from celestial fire (which is quite devastating). After you kill the 2 ferrikkis it should be easy to beat Malfarian. Also make sure you don't beat Behemoth first (the big guy that blocking the way to new area) before you build blacksmith and have all vinethorn gears you want because all monsters, including all bosses and nameds will become much stronger after you beat Behemoth and you wouldn't want that, especialy if you're still in the process of collecting resources.

Thanks, I've been beating the 2 ferrikkis no problem but then when I'm fighting him his celestial fire or ability almost one shot my pets. It could be because my pets are only level 64 at the moment I think?

That could be a factor as well, but if I remember correctly I beat him before hitting lvl 65. I did buy all vinethorn gears I need from trade broker though which made the fight became much easier. I have been using 2 air attackers and 1 light tank set up since then and it works quite great for me so far. 1 air attacker 1 light support and 1 water tank might work better later when nameds difficulty is increased again for later stage.