Buy Rank 31

Buy Rank 31 is a Premium Upgrade for BTD4 and BTD4 Expansion. It costs 12 to use. It immediately increases your rank to rank 31 without having to pop any bloons. It gives you all the towers including their level 4 upgrades as well as all of the game modes. too.

Trivia

 * In the expansion, this upgrade doesn't unlock the level 4 upgrades for the Spike Factory and Dartling Gun