Anyone here struggle with swamplands?

Wasted 3 groups so far.Its frustrating.i've been moving around abiltiies such as 25% mobility and cleansing fire.

I assume you're running in random comp. So, prioritize survival, specifically evades. You don't want to get hit, especially by the heavy attacks. Depending on your weapon(s) you have additional options you can use (for instance, Burning Retreat). Also make sure not to phase him on 25% if you have someone downed/dead. You can carry that fight, but you need to be very careful. Cleansing Fire is a waste btw.

Or just run in a meta comp and burn him down in no time. ;)

If you're vs. the Afflicted instability, get off a water staff 5 during the split phase to help your terrible pugged party members who didn't bring cleanse (try to combo into earth from water going back into your dps rotation, as Lahar actually does somewhat respectable damage)... It goes a long way, especially when he starts doing the poison rain. Dropping Sand Storm on all the trash mobs during the split can also take a great deal of pressure off of your party.

And then like Faenor said, just play it super safe yourself... You can't carry if you're going down, and you can never rely on pugs to be able to rez you without getting stomped into oblivion by the boss. Take icebow instead of hammer, arcane blast instead of primordial stance, and just stay at max range the entire fight... Dodge his charge/stomp, etc.

If you are PERSONALLY struggling with conditions where you need feel like you need to take Cleansing Fire, maybe try bringing Ether Renewal instead... The heal is pretty terrible, but the low cooldown at least makes it somewhat effective vs. Afflicted.

ok i actually brought fiery greatsword.