Lets see...
Tools I use when playing my trolls against stuff you're facing...
Khador Colossal - Throw Mulg with the Axer's Animus 14 inches across the board into the Conquest. Mulg can usually take the beating and crumple half of the Conquest with very little issue
Death Star - Dire Troll Mauler or Mulg with Wild Aggression the free boosted die will help you hit them, yes they're still going to get tough rolls, but as a troll player you should have an idea of how often you make tough rolls

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The other alternative I've found for single wound "death stars" is to throw the Mountain King at them with the Storm Troll's animus on him. Sweep if you can, take out as much as possible, and then hit them and electro leap on to other models.
Again, this is coming from a Beast Heavy player. I almost exclusively run eDoomshaper with Mulg, a Mauler, Champions, Krielstone Bearers w/
UA, and then fill out with Whelps, Fell Caller, and w/e I want.
Grey Templar wrote:Mountain Kings are still on the fragile side of Gargantuans. Two heavies can easily total him.
Colossals are vulnerable to getting jammed by infantry. Get some Kreil Warriors up in its grill, but spread them out so it can't engage them all, and you should be able to tie it up for most of the game. You don't need to kill it. If you can tie up 19 pts of his army with 8-10 points of yours its a good trade. Tough will be really annoying for it.
Mulg the Ancient is an amazing beatstick, especially with eDoomy. With a threat range of Yes. He can put a huge dent in a Conquest.
My Mountain King has been extremely durable and has yet to die in the half dozen games he's played in, but if your opponent dedicates 20 points, of course they're going to be able to easily take him down

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Agreed about tying up the colossals with Infantry, but then again my MK doesn't mind taking a turn to chew through a unit, I have other big beasties to handle everything else.
Mulg is always a beatstick

A 12 point model that is easily worth 15 to 20, and nothing says hello like throwing him 12 inches across the board with 2 inches of reach and the occasional Goad