Heroes are a tower category in Bloons TD 6 and Bloons TD Battles 2. Unlike other towers, the player is only allowed to choose one Hero to use in a game, and the player cannot place multiple copies of that Hero. Rather than having upgrades, Heroes gain XP at the end of each round and level up upon reaching certain thresholds, increasing their strength and/or unlocking new Activated Abilities, up to level 20.
Heroes gain XP at the end of each round. The amount depends on the round, with higher-numbered rounds giving more XP. Most levels take more XP than the previous level, though in BTD6, levels 12, 14, and 19 take less XP than the previous level, and level 20 takes less XP than level 18. Since the amount of XP earned per round and amount of XP it takes to level up both increase over time, the number of rounds it takes for a Hero to level up stays roughly the same throughout the game if placed on the first round. If placed later in the game, Heroes will initially level up faster than normal due to the rounds giving more XP relative to their level, but it normalizes as the level approaches the usual value. At any point, the next level can be unlocked instantly by spending cash, at a rate of $1 per 1 XP.
In BTD6, the amount of Hero XP earned at the end of each round is the same as player XP and tower XP outside of freeplay and Knowledge modifiers. Like player and tower XP, Heroes gain more XP and level up faster on higher map difficulties; 1.1× faster on Intermediate, 1.2× on Advanced, and 1.3× on Expert. If multiple Heroes are in play (via Co-op or the Bloons TD 6 Birthday Partyquest), the XP earned on each round is divided evenly among each Hero.
Note: the number of rounds to level up assumes the Hero was placed on round 1 and there are no other Heroes on the map.
All Heroes have an "XP curve" that determines how much XP each level requires. The curve is a multiplier to the XP requirement of each level (rounded half up), so a higher multiplier means the Hero levels up more slowly.
In Battles 2, all Hero Alts have the same XP curve as the Heroes they are derived from.
Most Heroes have at least two Activated Abilities: one unlocked at level 3 and one unlocked at level 10. Some Heroes have a third ability unlocked at level 7. In general, the level 3 ability is weaker and has a shorter cooldown, the level 10 ability is stronger and has a longer cooldown, and the level 7 ability is situational. All Heroes' level 10 abilities are enhanced at level 20. Geraldo is the only Hero to lack any abilities.
List of Heroes
Bloons TD 6
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