Set in a swamp, this map appears to be the home of Bloonarius. There are two lanes for bloons to go through. Bloons will usually take the longer lane encompassing the left side of the map. On prime-numbered rounds starting from 3 (e.g. 3, 5, 7, 11), swamp holes open and Bloons take the alternative, shorter path traversing the right side of the map.
During Boss Bloon Events, Bloonarius and the Bloonarius Minions spawned from it take a special path, starting from the normal entrance, following the left-hand path, then crossing over the rocks and following the right-hand path to its exit.
The two paths are separated by a tree and a column of rocks, which block towers' Line of Sight. However, left-side Monkey Subs shooting at the entrance due to Advanced Intel are able to curve around the rocks with their Moderate Seeking to reach the right path if set to First.
Tapping on the lake to the bottom-left of the top-right tree for approximately 25 times will summon a crocodile that does nothing to the bloons.
For a number to be considered prime, it must be a natural number greater than 1 that is not a product of two smaller natural numbers. Note that Round 2 is excluded from this mechanic; the first prime round that activates the portals is Round 3.
- Affected rounds from 1-100: 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89 and 97.
- Affected rounds from 101-200: 101, 103, 107, 109, 113, 127, 131, 137, 139, 149, 151, 157, 163, 167, 173, 179, 181, 191, 193, 197 and 199.
- Affected rounds from 201-300: 211, 223, 227, 229, 233, 239, 241, 251, 257, 263, 269, 271, 277, 281, 283 and 293.
- Main article: Bloonarius Prime/Strategies
Bloonarius Prime suffered from a severe bug upon its release in Version 27.0.
- Reverse Mode on this map was bugged on its release. On the prime number rounds, the bloons erroneously spawned out of the puddle where the prime and non-prime paths split, instead of the right-hand exit as intended. This gave the prime-numbered rounds only 1.4 Red Bloon Seconds, the lowest in the entire Bloons TD series. Patch 27.1 a few days later corrected this bug.
- The map's name, Bloonarius Prime, is a hint at its unique mechanic on prime-numbered rounds. According to Ninja Kiwi's 30th July 2021 blog, this was planned long before the creation of the map.
- Despite 2 being a prime number, it is not affected by the map's mechanic, possibly for balance reasons. However, spawning the round in Sandbox Mode will send it down the prime number path.
- When MOAB class Bloons enter the Swamp hole, they shrink down to nigh invisibility before coming out of the other Swamp hole.
- The two rocks above the log are treated as a path, with track based items and attacks being placeable there. However, the only time Bloons ever go there is during a Boss Event, where the Boss and any Bloons spawned by the boss will go across the rocks to the right side instead of going down.
- Bloonarius Prime is the only map with a boss-exclusive path.