Boss Bloon Event/BMC/Vortex

Overview
Vortex is an event in Bloons Monkey City consisting of a single battle against a boss bloon, Vortex: Deadly Master of Air, as well as additional bloons that spawn throughout the battle. It first debuted on 8/19/15. The event lasts for 7 days and is linked to the Bloon Beacon, as defeating the Bloon Beacon tile is essential for activating the event.

To access the boss the player must defeat the tile where the beacon is located. The player then has 1 hour to battle and attempt to defeat Vortex. If you fail to defeat Vortex within that hour, it will regenerate back to full health, and the cost will not reset.

Like Bloonarius, Vortex has its own unique battle tile (though it occupies no location on the map; access is through the event tabs on the right of the screen) which appears to be a grassy cliff. Vortex spawns through the top left enterance and normal bloons spawn through the top right enterance.

The player starts with 2 times the cash than a normal tile (including bonuses such as Magic Coin Purse), and supply crates also give double cash. Throughout the battle bloons will also file out of the starting point. At the top of the screen is a life bar for the boss with skulls marking 25%, 50% and 75% health. When those points are reached additional bloons are spawned at Vortex's current position, the difficulty depending on Vortex's level, including MOAB's (and higher). The battle consists of a single round (which does appear to be subdivided into a number of actual rounds for purposes of Banana Farms, Cuddly Bear, etc.; see Strategies) and ends either when Vortex runs out of life (success), reaches the exit (failure), or enough lesser bloons reach the exit to take the player down to zero health (failure). However if you do fail, any damage dealt to Vortex will carry over to the next attempt, assuming there is sufficient time. Damaging Vortex does appear to generate cash.

Vortex has at least 25 levels (there are no additional bonus rewards after level 20 and an achievement for level 25 and, at this time, no reports of a final level to the event), with difficulty and level increasing every time it is defeated. The cooldown of Vortex is essentially linked to the Bloon Beacon (which has a 6 hour cool down). This means defeating twenty levels will take a minimum of 5 days plus the amount of time for each level's battle with the boss, excluding bloonstone recharges to the Bloon Beacon.

Reattempts
The initial attempt is free, however if you fail you will have to pay a fee to try again. The second and subsequent tries on Vortex during each 1 hour window cost cash. The amount is calculated by this formula:


 * Cost = max((Attempt_number-1) * (Attempt_number-1) * 100 * Vortex_level, $50000)

For example, if it takes 6 attempts to take on level 17, the attempts will cost:


 * 1st - free
 * 2nd - $1700
 * 3rd - $6800
 * 4th - $15300
 * 5th - $27200
 * 6th (and subsequent) - $50000

Rewards
In addition to the standard 5 and cash for each defeat, bonus rewards are given for beating the following rounds:

Unlike normal tiles, the player is not awarded bonus Bloonstones for finishing with no loss of life (NLL).

Strategies
For strategies, see Vortex: Deadly Master of Air.