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this may seem like a stupid question but can i biomorph stranglers and impalers?
if this is the case, i can see a S7 flame template!
to do this, you need a seeding swarm.
take the brood, give it toxin sacs for S4, Ferocious for S5, upgrade to Big mutant for S6, and add +1S for the Web itself! What a weapon that can auto-kill a comissar, but the points are too much to be worth it. still, that's wounding a horde of Orks on 2+ with a crappy save. do the math.
Seeding Swarm Deathbringer: 16/5/13
Witch Hunters: Currently in development.
i take it by big mutant you mean exceptional size. If yes, then no, you cant. A model can only have one of those mutations be it hive node, size, weapon or acid blood.
As for the rest of the working out, you coud have a S6 flame template. Of course you can biomorph them, otherwise you'd only be allowed squads with them of up to 8. Hell, now i think about it that's probably enough. If you did use a squad tho, i dont think you could have toxin sacs for +1S. Might want to check that.
Anyway, who uses those weapons? I've nly ever seen them on the GW website
As monsieurcartier said, a model may only ever have a single Mutation. Since fielding Stranglewebs and Spike Rifles separately from Strangler and Impaler broods requires them to be Weapon-Beast Mutants... You quite clearly can't combine ExcSize and WB Mutations on a single model.
As far as Impaler and Strangler broods go, they can not be given extra Biomorphs. Yes, they're listed as "Mutable Genus"... However, I take this as a simple reference to their basic Genus stock, the Gaunt. There are no Mutable Genus tables to create Infiltrating Gaunts such as the Impalers and Stranglers, nor are there the required normal bioweapon costs for the Spike Rifle and Strangleweb. All the costs listed on CA are when fielded as WB Mutants or as part of the special broods with "Infiltration" which we don't know the pointscost for.
People have disagreed with me on this in the past, and they're free to do so. IMO the situation isn't clear enough to allow for assuming that they can be Biomorphed as per the regular Mutable Genus rules, and thus I vote against it.
"The meat things seek to destroy ourselves. They hunt us as we hunt them but they are weak and uncertain. The inferior flesh will be entirely destroyed, all biomatter consumed. Ourselves will fight to the last, all weak flesh must be devoured."