Challenger Deep

 is a brand new track released on the Christmas update (version 2.3). 250,000 pops are required to play on this track.

Overview
A desolate ocean along with small islands are there. Monkey Buccaneers and Monkey Subs are a high recommendation on this track since there is barely any land. However Sniper Monkeys, Mortar Towers, Dartlings, are all still useful.

Tips

 * Monkey Buccaneers, Monkey Subs and Dartlings are important if the player doesn't want the Bloons to leak.
 * Pontoons are a good choice too, since this track does take place on an ocean. Pontoon pros would be even more effective since they increase the range of any towers place on top of them.

Trivia

 * This track references the real-world Challenger Deep, a depression on the bottom of the Marianas Trench. The Challenger Deep is the deepest part of the world's oceans, at 10.916 kilometres (approximately 6.783 miles) down.
 * This is currently the most water-filled track in the Bloons Tower Defense series, a title formerly held by Archipelago. However, Flooded Valley from BTD6 with the secret flooding effect purchased exceeds it, having no land available whatsoever.
 * Despite the track itself being fairly long, due to lack of land, it is placed in Advanced difficulty.
 * The track bears some similarity to the map for the Submarine Alliance mission in Bloons Monkey City Mobile.