Once you start, you cannot stop. Bloons will keep coming until you lose. How far can you get?
~ Description in BTD5 when mouse scrolls over the Apopalypse Mode icon
Apopalypse Mode is a special mode in all versions of Bloons TD 4, Bloons TD 5, Bloons TD 6, in which there are no breaks between rounds. The cost of towers and upgrades is the same as in Medium Difficulty. Income is not earned by progressing from one round to the next, but only from Banana Farms and popping Bloons. The difficulty and number of Bloons in Apopalypse Mode also increases as the player progresses to higher rounds.
Apopalypse Mode has a B.F.B icon in BTD4. In BTD5, this was changed to a skull and cross-bones on a Black Bloon. This mode is unlocked at Rank 31 in BTD4 and BTD5, but Rank 36 in Bloons TD 5 Deluxe. In Bloons TD 4, this mode has infinite rounds; in Bloons TD 5, it only has 400 rounds. In BTD6, Apopalypse mode is unlocked per-track. To unlock it, the player must beat Medium difficulty on said track to unlock Military Only for that mode. The player then has to beat Military Only to unlock Apopalypse mode for that track ONLY.
The bloons that spawn from waves and spawns are random each time, and this gameplay changes quite a bit between each game. The earliest time possible for the highest type of bloon to spawn on that round is shown, but can vary.