I think Glenda’s a better choice than Frosth since she not only gives minions to all, but also buffs the special skill. The minion attack/hp boost that Frosth gives is not that important, since you’re going for special skill damage anyway. And you already have Ariel for the mana buff.
I would change the formation though, to cKrampus - Pengi - Glenda - Morel - Ariel since Pengi gives minions to nearby, and Glenda’s buff serves Morel better.
My Pengi team is cKiril - Krampus - Frosth - Pengi - Thorne (in that firing order). Because you can’t control who Pengi fires at, Thorne is there to finish off any survivors. I’m levelling up a 2nd Pengi to replace Thorne in the near future. Troop-wise, I gave Pengi a ninja troop for the bypass chance.
And I agree, it’s a really fun team if you get the 9 tiles
Edit : If you want to add Frosth so that your team has 15 minions when Pengi fires, then I’d take out Ariel. When you get 9 tiles, you won’t need healing