My pick is letting Sylvia (the meatslab with an axe) come along or at least persuading her to come because it seems Remi is physically weak to count for stronk magic. Then be a proper hoonta and put traps around the Mantis's lair and smoke em out.
Go into the catacombs ofc. Maybe have a sort of meat tank with Sylvia and have Remi move in stealth behind. When Sylvia engages the lizardfucks, Remi ambushes with crowd-control spells.