After finishing Slub Gut's Sanctum (5), Melvin takes you to the multiplayer arena and offers to give you the Adventurer's Starter Party for free. I had already played several multiplayer matches and bought the Holy Healer pack. Two problems followed: (1) I ended up being charged 50 pizza for the Adventurer's Starter kit. (2) Melvin promises that you will be playing a match against him — I ended up getting matched with another player. For what it's worth, after I finished my match with another player, I went back to the Starter Shop where it had the Adventurer's Starter Party listed for free (I am still short the 50 pizza).
