Bloontonium

"Bloontonium. The mysterious material that infuses Bloons with their power. Some would just wield it against their fellow Monkey Cities. The only viable deterrent is for you to join the arms race and build your own Bloontonium Generator."

- "Precious Precious Bloontonium" Quest description from Bloons Monkey City

Bloontonium is a radioactive substance that is used to create Bloons and allows some attacks to ignore all bloon immunities. It is first mentioned in Bloons Tower Defense 5 and makes further appearance in Bloons Monkey City, Bloons TD 6, Bloons Adventure Time TD, and Bloons Pop!. Bloontonium makes a real appearance in both Bloons Monkey City (including Mobile versions) and Bloons Pop!.

Bloons Monkey City
It makes its real first appearance in Bloons Monkey City, and has one sole use, to send Bloons at other players in Monkey vs Monkey. Battling with other players requires use of Bloontonium to send bloons. Different versions of the game deal with Bloontonium storage and sending differently.

In Flash, Bloontonium is created from Bloontonium Generators, and stored in Bloontonium Storage Tanks. Every time the player wins a defend battle, the amount of Bloontonium acquired is the same as how many Bloons they popped in that battle. More Bloontonium used sends stronger bloon waves, up to slightly more than the maximum possible capacity relative to the offender's level. Bloontonium can also be bought with Bloonstones for 1 per 40.

In Mobile, Bloontonium works different. Sending bloons in battles is organized by the Bloon Inflation Factory, and the tank must be at least 100% full in order to make a send. When the Bloontonium tanks exceed their maximum capacity (over 100%) they will shake, and can only store up to 200%; this is only possible by collecting excess Bloontonium that was not automatically generated by the factory. Bloontonium can be bought with 1 per 2.

Bloons Pop!
In Bloons Pop!, Bloontonium instead appears as some kind of red liquid substance in a canister and is used to produce Bloonstones. It can be gained by winning games, at a rate of 50 per game plus more from Golden Bloon Time. This value increases by +50% if watching an ad.

Trivia

 * Bloontonium is a play on the word Plutonium (Pu).
 * The only items that are references to Bloontonium in Bloons TD 5 are Depleted Bloontonium Darts, Bloontonium Lab, and the Bloontonium Reactor for the Monkey Sub.
 * Bloontonium is a radioactive element and so often carries the radioactive hazard symbol on its container.
 * According to the Bloontonium Mine in Bloons TD Battles and the Bloontonium Generator in Bloons Monkey City, Bloontonium can be both mined and generated.
 * Due to Bloontonium being able to make Bloons but also destroy them, their true purpose is unknown.
 * Due to Ground Zero and Tsar Bomba's nukes being nuclear weapons and Bloontonium being the main radioactive substance in the series, the nuclear weapons being used in the Ace's abilities may be Bloontonium bombs.
 * According to BTD6's Hydra Rocket Pods' description, it uses depleted bloontonium for the Dartling Gunner's rockets. This means that the missiles may be micro nukes.
 * Depleted Bloontonium may be the specific type of Bloontonium the Monkeys use in their weapons, due to the amount of times it specifically says "Depleted" in the upgrades in both BTD5 and BTD6.
 * The character Commander Cassie from Bloons Adventure Time TD has an upgrade called Bloontonium Tips, which just like it did for Depleted Bloontonium Darts in BTD5, makes all attacks able to pop any bloon type.
 * There is an exploit in Bloons Monkey City Mobile (including Steam version), where the player can speed up a 99% filled Bloon Inflation Factory for no cost at all.

Blog posts
US$
 * According to Ninja Kiwi's 9th July 2021 blog, different types of Bloontonium can have different colors depending on where the Bloontonium is harvested from.
 * Accroding to Ninja Kiwi's October 8th 2021 blog, bloons and blimps are inflated with Bloontonium, and the substance itself requires high-tech laboratory standards to properly handle such a dangerous substance.
 * According to a user question posted on Ninja Kiwi's October 29th 2021 blog, it is not possible to earn exactly 69 Bloontonium in a single Bloons Pop! game. Ninja Kiwi replied that this is how the formula works, but this absent number 69 is likely done to avoid sexual references.