@ OP and everyone else...
I was encouraged by my local meta to chime in on this forum and thread, after debating the effectiveness of the Mountain Troll at length, and facing it on the table. I think this piece is much better than the Troll players are giving it credit for; and I will consent that there are some general issues with the Gargantuans with regards to efficiency of Fury per point, and battlegroup balance. However, the survivability of this thing is off the charts and that is the real value of this 20 point model...
The ability of a piece to get to ARM 23 is no small deal. I know the poo poo on the idea of leveraging 16 points to get it there, and the claims that it's not worth it. I disagree, on many fronts, mostly in that ARM 23 IMHO is not just tough to deal with (pun intended) but threatens the balance of the game. Going over ARM 20 is where problems begin, being able to be there reliably on a piece that has this many boxes and the max healing ability means that a list built and designed to take advantage of this will be near impossible to beat in many scenarios games. It's intended to be able to be a reactive piece, that dictates opposing board position, and that plays right into the hands of the brick style that Trolls takes advantage of better than any other faction. I know that is going to garner criticism; however think about it. Let your opponent break on your ARM 23 48 hit box, healing model. Then retaliate, feast on what is there, heal, and grind. Rinse and repeat. He is nearly a win condition unto himself in a strong list.
I have heard and read the critique that it doesn't deal the damage that most would expect. I'd argue that is the case for all the Colossal and Gargantuan. They have the ability to mow thru infantry, and I think the expectation was that they would be heavy jack and beast killers. The fact that this thing can thresh, and heal on boosted attack rolls is off the charts redonk. He can then spray, and use the left over Fury to burn more infantry. All the while snacking and healing.
You need two POW 20 Heavies to have a prayer of killing his thing in one turn, assuming the aforementioned ARM 23. Not being able to trade pieces for this piece in one turn is the single biggest advantage it has; and as a beast (meaning it's nearly always fully functional), especially with it's healing ability, the advantage is significant. This game's balance is based on how models impact the game, and what it take to remove them. When playing games, the key consideration we make on each turn is what it takes to remove threats off the board. The reality is that when you can dial one of these things up to the point where they really can't be removed in one turn, that is an issue that warrants serious consideration.
A lot of argument in my own meta stemmed from the fact that the ARM 23 is only useful if you continue to "brick", making it so you could not go out and threaten your opponent; however, I would say that is exactly the way to do it. They will have to feed you infantry or pieces at some point, and you take what they give you, mow through what is there, and brick up again. The constant ARM 23 will wear your opponent down, and that is the ultimate argument for this piece being very viable.
The usefulness of the POW 16 RNG 10" is really being overlooked. I know the RAT is poor, but you have to always consider the boost is essentially part of it. That changes things. He can trample and use the spray, charge and use the spray, spray out of combat, etc. The spray gives him the unique ability to remove key UAs and solos that were otherwise hidden, or unreachable.
IMHO opinion, there is something hidden in the Gunbjorn list with this guy. Mountain Troll, Rok, and Earthborn, start with those 40 points, and I bet you have a very formidable start to a really excellent skew list that nobody is going to believe works well at 50 points and up.
Overall I don't expect most to agree, but consider the survivability, the board control, and the spray. Play test the piece. Please note, I'm NOT saying there is no bad matchups or that no list can handle this. I'm simply suggesting that the Mountain Troll offers much more consideration than I feel Troll players are giving him credit for currently. He very much has a role in many 50 point lists and higher, as well as on the competitive table. It's no skin off my back if Troll players en masse decide not to play this guy, in fact that works just fine for me

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A.