The Vault is a selection of almost impossible challenges that is unlocked after defeating an impoppable mastery on an extreme map. The four challenges are designed to see your knowledge of different mechanics in the game.
Challenge One Edit
"For people who use powerful upgrades/towers for a low price"
The First Challenge is on Hard on 3 Times Round. It disables towers or upgrading a tower over 1,000 (Stacks). You also can't spend a total of 10,000 over all your towers. You start with 10,000 cash and start on round 75, good luck!
Challenge Two Edit
"Impoppable not so hard? How about even more difficult Impoppable?"
The Second Challenge is Impoppable on Jungle. It consists of 89 rounds, the first 85 are normal, only with upgraded balloons. (More speed, health (If takes multiple hits) And if a Camo or Regrow, it will be a Camo and Regrow. But the last 4 rounds will go the same but finishing with a Boss Balloon (Bloonarius the Inflator, Vortex: Deadly Master of Air, Dreadbloon: Armored Behemoth and Blastapopoulos: Demon of the Core, all in this order).
Challenge Three Edit
"The ones who never struggle with extra properties."
The Third Challenge is similar to The Convert Pops special mission, only far beyond difficulty. Except the fact is is on Bloontonium Lab, difficulty is set to impoppble, balloons are upgraded by one tier and are Camo Regrows!
Challenge Four Edit
"The Ultimate Test!"
The Last and most difficult challenge is far beyond the other three, It combines all three into a single challenge. You can't spend more than 10,000 on a Tower and 200,000 on all your towers. It goes to 104 (Last four have the bosses like challenge two). It is on Bloontonium Lab in Impoppable with just Camo/Regrows with the upgrades, (Challenge three). Agents are disabled and set to 1 life only. Unlike the other challenges, you cannot save and do it in separate parts.