Hard Difficulty is the third and final difficulty in the Bloons Tower Defense 2-5 (not BTD5 Mobile) since the release of Bloons TD 2. At the beginning of a game, the player has half as many lives on hard as they do on Easy. In BTD2 and BTD3, hard difficulty has 50 Rounds. However, purchasing the towers is also pretty expensive in hard difficulty.
In Bloons TD 5, the player must pass Round 85, which is the first round with a ZOMG bloon, in order to win on hard difficulty. The Bloons move a little bit faster than on Easy Mode or Medium mode, and the player has only 100 lives. Towers are 8% more expensive than in Medium Difficulty. This difficulty is represented by a Robo Monkey, or by a Sun God in Extreme Tracks in its icon.
In Bloons TD 6, the player must pass Round 80, which is the first round with a ZOMG bloon, in order to win. The player also starts on Round 3, meaning the player gets 2 rounds less of cash, sarting with only $650. Towers are 8% more expensive, and the player has only 100 lives. There are also a lot of variations based on Hard difficulty.
Alternate Bloons Rounds: All rounds are slightly harder as some bloons are replaced with tougher variants.
Half Starting Cash: You start with $325 cash instead of $650. You will start with $425 instead of $850 if you buy the Extra starting cash Knowledge.
Impoppable: One life, survive until Round 100, very expensive towers. Similar to BTD5 Mobile's Impoppable mode, but you start at Round 6 instead of 3.
Double HP MOABs: All MOAB-class bloons have double health.
CHIMPS:(No Continues, Hearts lost, Income, Monkey knowledge, Powers, Selling). Extremely similar, but not identical to NAPSFRILLS. The hardest mode in the game, survive until Round 100 with these rules. You start at Round 6.
Sandbox: A mode to test out strageties in different tracks, difficulties, bloon rounds, and towers. No rewards whatsoever in this variation.