The Mawloc wasn't that bad against my fnp terminators - it failed to clear a path twice (although it took out my champion and two of my combi melta's). It kept going into ongoing reserves though so it kept coming back.
I took casualties everytime it turned up.
I think its one to use to kill a squad of meq/geq. And with LoS as Sethis said above, try to avoid characters