The Great D.E.P.R.E.S.S.I.O.N.

The Great Deadly Economic Plummet from a Rich Entity that Steals Salary from InnOcent moNkeys, or Great DEPRESSION, is a boss that appears on round 1939 and is the mother of all Pennypincher Bloons.

Before the fight
It craves money so much that its very presence will cause everything to be gradually drained of money. Starting on round 1929, very bad things will start to happen.
 * On round 1929, the player will earn 20% less cash from popping Bloons and Pennypincher Bloons will be much moar common.
 * On round 1930, alternative sources of cash will disappear 20% faster and earn 15% less money.
 * On round 1931, an extra K.R.A.B.S. will start appearing with every round until round 1939 and all non-MOAB Class Bloons will have the Greedy Property.
 * On round 1932, the player will earn 30% less cash from popping Bloons and effects that earn more cash per Bloon pop will become 40% less effective.
 * On round 1933, moar Pennypincher Bloons will start appearing and alternative sources of cash earn 25% less money.
 * On round 1934, the player will earn 60% less cash from popping Bloons and effects that earn more cash per Bloon pop will become 70% less effective.
 * On round 1935, 2 more extra K.R.A.B.S. will start appearing with every round and alternative sources of cash will disappear 50% faster.
 * On round 1936, the player will earn 80% less cash from popping Bloons and effects that earn more cash per Bloon pop will be completely nullified.
 * On round 1937, an extra M.O.A.R. Bloon will start appearing with every round and EVEN MOAR Pennypincher Bloons will appear.
 * On round 1938, every source of cash will be completely nullified.

Round 1938 is a rush of 50 Pennypincher Bloons, then a rush of 20 Shielded Regrow Pennypincher Bloons and a Speedy K.R.A.B.S., then a semi-rush of 10 Heavily Armored Pennypincher Bloons. After that, 15 K.R.A.B.S., then 6 M.O.A.R. Bloons, and then a King M.O.A.R. Bloon.

The Actual Fight
The Great DEPRESSION itself will have a health of 500,000. Upon appearing it will destroy all money-generating towers on screen, increasing its health by the total cost of the towers it destroyed and stealing the money. It moves at 2/3 the speed of a Z.O.M.G. and is twice as big as the M.O.A.R. Bloon. When destroyed it releases 20 M.O.A.R. Bloons. It is assisted by an invincible Sponge God which will attack your towers. It is also immune to anything that costs moar than $20,000. Its attacks drain critical amounts of money and it will always increase its health when it steals money. Its weakness is fire-based attacks and it will take double damage from those.

Phase 1
Attacks:
 * MOAR! MOAR! MOAR!! (passive) - Any towers in the radius of a 0/2 Super Monkey will be downgraded once every 3 seconds and it will steal whatever the upgrade costed. Any unupgraded towers in this radius will lose 1 HP every second. It will also steal $20 from you every second.
 * There's a standing fee! - All towers that aren't doing anything will lose 'ALL of their upgrades and have their health set to 1, unupgraded towers that are affected will just be destroyed. It steals whatever the tower/upgrades costed.
 * How I love thee! - Deals 50 damage to your most expensive tower and steals whatever it costed if it gets killed by this.
 * Ultimate pennypincher - Surrounds itself in a yellow forcefield for 10 seconds. During this time, it will steal $20 for every damage it takes.
 * Don't burn me dollar! - Fire-based attacks will bounce off all Bloons and hit your towers instead for 10 seconds. After that it will deal 20 damage to any towers with fire attacks and steals whatever they costed if they die.
 * FREE...FOOOOD?!??!? - Destroys any towers that make upgrades free and steals whatever they costed, as well as getting rid of all unused free towers.

Phase 2
When its health is lowered to 200,000, it will become invicible and immobile and the glass containing its money will crack and get a hole in it. For 10 seconds it rapidly leaks out gold pieces which can be collected for $300. After that, its eyes will become red and angry and it will release Round 1938 but at its current location and all Bloons spawned have double health. Pennypincher Bloons will also not be able to use their Pennypinching ability. Because of that they will be very angry, moving at twice their normal speed. Afterwards it will teleport back to the entrance in a yellow flash and continue normally, but with twice its original speed. It also gains new attacks:
 * What don't you understand about MOAR? - Sacrifices 50,000 health and summons a Heavily Armored M.O.A.R. Bloon. Only used once.
 * Sponge God: MAXIMUM POWER!!! - The Sponge God will start to glow yellow as it yells the quote 'MAXIMUM POWER'. It then fires a 30 degree sweeping laser in front of it which deals 20 damage to anything it touches.
 * Jellyfish Storm - The Sponge God summons a portal which releases a powerful jellyfish storm, dealing 50 damage to all towers on screen. The Great DEPRESSION steals the money from any dead towers.

Death Animation
The Great DEPRESSION will become immobilized, shaking. A few seconds later, its glass will completely shatter, spilling gold pieces everywhere around it for 15 seconds. It will then burst into flames as white light starts emerging from it. The Sponge God assisting it flees, becoming a free Pro SpongeBob for you to place down at any time. The Great DEPRESSION will explode into fire, leaving behind all the money it stole from you and its children, 20 M.O.A.R. Bloons. No more Pennypincher Bloons, K.R.A.B.S, or M.O.A.R. Bloons will appear for the next 20 rounds afterwards.

Backstory
You will be able to see the backstory of the Great DEPRESSION once you get the achievement for popping 1,000,000 Pennypincher Bloons, 'No pinching allowed!' ''The Bloons noticed that they released cash when they were popped by the monkeys. They got an idea to do the opposite and create a special blimp that stole money every time it was hit, known as the Pennypincher Blimp (PpB). It was programmed with a special mind that hacked into the monkeys' supply of money and was powered by the enemy attacks.''

''This was successful, and even though the PpB was destroyed by the monkeys, it gave the Bloons a substantial boost in money, enabling them to produce even more of that blimp and better versions as well. This resulted in a vicious cycle which the Bloons would soon regret.''

''One day, the Bloons created the strongest variation of the PpB to send at the monkeys. This is, of course, was the Great DEPRESSION itself. However, it had a flaw in its programming, causing it to become self aware. It attacked the Bloons and stole money from them, making itself even stronger. It eventually got tired of the Bloons and left. So the Bloons decided to never use something like that again.''

''However, it had already horded massive amounts of money. It created its own offspring, the Pennypincher Bloons, to remotely deliver cash to it. Because of this, it could get much richer and produce even more offspring. It decided it would create its first blimp as its offspring. It got inspiration from the television cheapskate known as Mr. Krabs. And so it created its first blimp, the K.R.A.B.S. This new blimp helped it earn lots of money and eventually create new offspring, like the Greedy Bloons and the M.O.A.R. Bloons.''

''Today, the Great DEPRESSION has collected unimaginable amounts of money, robbed countless monkey kingdoms, and ascended to be the ultimate cash thief. But everyone is aware. The story has been passed down through many generations. Many have worried about it or are looking for a way to finally defeat it. Do you have the skills to hunt down and destroy this overly greedy menace? I don't think so, but good luck anyways.''

Trivia

 * I worked on this for nearly 2 hours...
 * Its effects start on round 1929, the first year of the Great Depression. It appears on round 1939, the last year of the Great Depression.
 * Lots of the attacks reference SpongeBob SquarePants episodes.
 * This is a joke, but not really.
 * nothing else