Test Bloon

The Test Bloon, also referred to by some fans as the Ghost Bloon, is a Bloon that only appears in Sandbox Mode in Bloons TD 6. It is an outline made of white lines. The Test Bloon cannot be encountered in any game mode besides Sandbox Mode; the main purpose of this Bloon is for testing how much popping power a tower has, as well as for testing the activating of 'lost life' upgrades and abilities.

Properties
This Bloon moves as fast as a Red Bloon, and has 10,000,000 HP. Leaking the bloon will cost only 1 life. It has no immunities whatsoever but it possesses massive health.

Destroying
The Test Bloon can be destroyed instantly by certain towers, such as the following:
 * Druid of the Jungle's vine
 * Bloon Master Alchemist's shrink potion
 * Obyn Greenfoot's Wall of Trees ability
 * Bomb Blitz's Ability (Only when a bloon leaks)
 * Legend of the Night's Black Hole (Only when a bloon is about to leak)
 * Engineer Monkey's Bloon Trap and XXXL Trap
 * Psi's basic attack and Psionic Scream ability

Additionally, some towers have the means to eventually destroy the Test Bloon single-handedly:
 * Pat Fusty can, at level 17, reliably loop a Test Bloon indefinitely and eventually destroy it.
 * The Druid of the Storm upgrade can loop a Test Bloon indefinitely and eventually allow the Druid to destroy the bloon.
 * The Sun Temple or True Sun God with sufficient magic sacrifices can knock back the Test Bloon with its magic shockwave and deal enough damage to pop it quickly relative to other strategies.
 * 20 maximally buffed Sun Temples can pop a Test Bloon even without stalling it.
 * Ninja Monkeys can knock back the Test Bloon with the Distraction upgrade, thus creating an infinite loop and eventually popping the Bloon.
 * Ice Monkeys with both the Re-Freeze and Enhanced Freeze upgrades can indefinitely freeze the Test Bloon and eventually pop it.
 * Glue Gunners with the Super Glue upgrade can indefinitely glue the Test Bloon and eventually pop it.
 * Bomb Shooters with both the Bloon Impact and Missile Launcher upgrades can stun the Test Bloon indefinitely and eventually pop it.
 * Heli Pilots with the Downdraft upgrade or above can blow back the Test Bloon indefinitely and eventually pop it. Using the Special Poperations upgrade helps speed up the process.
 * Super Monkeys with the Knockback upgrade can indefinitely knock back the Test Bloon and eventually pop it.

Trivia

 * It is poppable by damaging it about 10 million times, but it would be a waste of time to try and do so.
 * It is currently not possible to spawn camo, regrow or fortified versions.
 * Ironically, the visual appearance of the Test Bloon is much less visible to the player than any Camo Bloon, while all attacking towers (both camo-seeing and non camo-seeing) can see it immediately as if it is a regular bloon.
 * Leaking this Bloon will only deduct one life, concluding this Bloon has 1 RBE.
 * It is a ten million layered Red Bloon as demonstrated by the Druid of the Jungle's Vine crushing it.
 * This is the strongest poppable bloon (other than than some levels of Bloonarius the Inflator) and technically the poppable bloon with the most layers. However note that monkeys with 'strong' targeting will target other bloons first, ignoring it until it is the final bloon on screen.
 * Starting on round 750, fortified BADs will have more than 10 million HP. However, they are not poppable, as they cannot be stalled and move at twice the speed of pink bloons.
 * Having a tower pop roughly 215 of these bloons allows that tower to reach the old maximum pop count of 2,147,483,647 (231&minus;1) which is the higher number that can be stored in a 32-bit signed integer variable. As of Version 9.0, the pop limit is now lifted higher than the 32-bit maximum, presumably to the 64-bit maximum. However, it currently is impossible to determine the new maximum number through in-game testing, as attempting to do so will eventually crash the game before reaching the new maximum number.
 * Video about the hero glitch being able to pop a test bloon.
 * The hotkey menu for BTD6 Steam actually refers to this bloon as the "Test Bloon".