Plan your time. It will take you longer than 30 minutes, without a doubt.
Split up and move carefully. Have one player who can solo the street mobs be the one to navigate, while others stay somewhere "safe". Not everyone has to talk to Marla...if any member of the group does, all players see the conversation and get credit for it. The mobs move in a path up and down the street in a circuit. Get on the side of the street where the mobs are moving toward where you want to be (like a Norton Tower), and, while staying on the sidewalk, walk right behind a mobs with the biggest gap behind it. Keep pace with the mob, but stay behind it. When you get to a spot where you can move off of the sidewalk safely (like the yard around a tower), have your friends teleport to you.
Remember, it's a dungeon. Players can leave to refill potion bottles and teleport back...just leave one player in the dungeon at all times to teleport to.
On the tower battle, save a potion for the top floor. Try to end each fight with as close to full health as possible. Before finishing the last mob on each level, let everyone cast a healing spell, then take it down.
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