****, thanks for mentioning the familiar possibility--our shardmind sorcerer just acquired a jankx familiar and I'm not used to adjudicating or planning for them. It's entirely possible he'll send the ol' sacrificial gerbil through first and I'll have to plan for that.
I feel like the tank will be first, but it could also be the rogue or even for some bizarre reason any of the others. Regardless of who comes through first, they're being subjected to this range of effects:
The grell gains a +2 bonus to AC while it has an enemy grabbed.
Tentacle Rake (poison) At-Will
Attack: Melee 2 (one creature); +12 vs. AC
Hit: 2d8 + 6 damage, and the target is slowed and takes a -2 penalty to attack rolls (save ends both).
Tentacle Grab At-Will
Requirement: The grell must not be grabbing a creature.
Attack: Melee 2 (one creature); +10 vs. Fortitude
Hit: 2d8 + 6 damage, and the grell grabs the target (escape DC 16).
Double Attack At-Will
Effect: The grell uses tentacle grab and tentacle rake, or uses tentacle rake twice.
Venomous Bite (poison) At-Will 1/round
Attack: Melee 1 (one creature grabbed by the grell); +12 vs. AC
Hit: 1d8 + 4 damage, and the target is stunned (save ends). The stun also ends if the grell is no longer grabbing the target.