The Tavern

Regarding a current run with a Naga of Qazlal IE / hybrid.

Strongest direct damage spell I have found is starburst, but I have found more effective the combination of Freezing Cloud + Airstrike to prioritize malmutators. Still, this usually takes 3-5 turns to kill a problem malmutator. To be fair, I have barely experimented with Qazlal's invocation powers in terms of alpha striking priority targets. Since I'm a Naga, breaking LOS with movement is frequently not a good option.

At this point in Pand. I have about 7 runes, and a collection of extremely nasty mutations with no potions of mutations left. Examining my gear, and list of spells, I don't see anything that could have prevented my getting all of these mutations for during a 15 rune run, short of abandoning my hybridization and pumping Fire magic and hoping to get Firestrike somewhere, there doesn't seem to be a lot of spells that can kill malmutators before they mutate you.

What is the best strategy for avoiding mutation in current version, considering movement is limited?

http://crawl.chaosforge.org/Neqoxec

cannot sinv

hide behind summons/enemies and use bvc+javelins or smite-spells like airstrike.
Malmutaters need a clear path of free space towards your position.

I concur with Nebukadnezar, but will also add that storm form's blinkbolt is also a very effective method if you're willing to take a little more risk. Weak malmutators can be instantly killed, but caco's might need an additional turn in smackdown, though not long since storm form hits really nicely.

Constrain LoS, kill them ASAP, and hope not to get screwed.

Sometimes an orc or w/e summons a malmutator and you can't kill it in 1 turn or break LoS easily. Best you can do is limit the chances of it happening.

Have fun in the new hell I guess?