Was it a critical hit, and how much does mauler usually hit's you?
You can have a look at new abilities monsters got very recently here: http://dragoneternity.com/about/news_innovations/9962.html#cP=1

Ihit, level 15 mobs only hit for about 150 on a normal hit, about 250-300 for a critical, but the lightning rod buff does about 400 on a normal hit and about 800 on a critical. And if they get 2 buffs stacked they can just instantly kill you no matter what
I too have died many times while trying to complete protector quests which now take even longer because if we summon dragons they are most likely to die and food is fairly expensive for them

At level 47, fighting 48 Darkguard inquisitors for PQ just now...

Normal "white number" physical hit from darkguard... 300-400 range
Critical "red number" physical hit from darkguard... 750-900 range
Normal "white number" lightning bolt hit from darkguard... 965-1050 range
Critical "red number" lightning bolt from darkguard... fortunately none today, but have seen 1800+ before and suspect it could easily go over 2000.

Those are from a single stack of the buff - it can stack twice, so double those numbers for actual damage possible. As said above, it is possible for an instant kill on round 2 of combat even when using flawless pots.

Something a bit wrong with this buff (and the description that it does 90% of normal damage).

As listed above, those are the regular numbers approximately. With the abilities they hit for 4 times that, and it can stack so double all of that o.O