*shudders at the thought of the title*

Anyway, I have a question regarding this creature.

It has a special ability called Monstrous Limbs. I want to make sure that I understand this correctly. I make one combat check against a PC. Based on just straight successes I use the damage from the claws, correct? Or do I get to choose which "weapon" I am using? And in order to add in the rest of the limbs I have to have the correct advantage?

I think Monstrous Limbs allows you to choose which of its three weapons you use for the initial hit (aka the Primary Weapon), while giving you the ability to spend the given results to score hits with either or both of it's other two weapons. Each weapon does it's own listed damage (plus successes as usual), and the qualities of each weapon that hits can also be activated (such as the Jaw's Crit-Rating of 2 and the Mawed Tentacle's Linked 1)

It references a combined attack, which is covered under Two-Weapon Combat (GCRB 108). Monstrous limbs both eliminates the penalty for making a combined attack, and allows you to use three attacks (instead of two).

Monstrous Limbs changes how Two-Weapon Combat affects the Merroid. First you choose which of the attacks is the "primary" attack, the one the merroid is focusing on; normally, you'd take the lower characteristic and lower skill among the weapons its attacking with, but since they're all Brawl-based, you'll just be using its Brawn characteristic and Brawl skill; Monstrous Limbs specifies that it negates the increased difficulty of a Two-Weapon Combat check, so it stays Average; finally, it specifies that you can then use Advantage and Triumphs to hit with either of the other two attacks, possibly both of them, just like regular Two-Weapon Combat.

Also, thanks to Mawed Tentacles being Linked, a good roll can result in four hits, something usually reserved for Auto-Fire weapons.