Into Round 2: Gro-More
Tut, the buzzsaw does d8. I was originally thinking d6+1, but d8 is fine. You buzz away at the Shambler with Marivhon.
Renwick, yeah, some monster lore would come in handy. Especially today, as it turns out that lightning makes Shambling Mounds GROW in size. They each gain 14 hp, and the Gardener makes his save, taking 7 more. You've got another round as they approach, plus two rounds now in combat, if you'd like to cast more Lightning Bolts their way.
Brogg in round 1 does 10 to the Shambler+ with Marivhon.
Into round 2, Brogg and Tut do a combined 23. Guys? Gotta save Marivhon...
Moth has two rounds (both in melee), Renwick has three rounds (2 in melee), Schmektor and Dave FoO have four rounds (2 in melee). Report in, and we'll go from there...