ACK! ZOMBIES! I'm with Leigh--some pipes are best left clogged! Maybe a plumber worthy of Plunjolnir will find my telescopes, drain these zombies, and claim the payday.
- Quest Log of Eve Strough
It is recommended that you use an Attack-class character with the Vampiric upgrade, or a character with a high amount of health such as the Oak when attempting this challenge. After collecting all secret invoices in the Town Center, head to the sewers where you can find Pack Rat and interact with the picture of a lady on one of the stairs. This requires 75 tacos. After that, pick up the Plunjolnir and defeat 15 Yeti Zombies that spawn. The game will give you a massive damage buff, so just fire away and it will deal massive damage, capable of killing the Yetis with little effort required. Don't die while attempting this challenge or you'll fail it. Once you've defeated 15 of them, the achievement should be unlocked.