Filibuster Invasion (フィリバスター襲来ステージ, Filibuster Attack Stage in the Japanese version) is a special stage in Cats of the Cosmos Chapter 3. It temporarily overrides a random stage after completing the chapter for the first time, much like a Zombie Outbreak. It can only be completed once. Upon completion, Filibuster Cat X will be unlocked.

Battleground
- 1 Filibuster Obstructa spawns as the boss after 1.67 seconds50f.
- 1 Bun Bun Symbiote spawns as the boss after 80 seconds2,400f.
- 1 Bore spawns as the boss after 10 seconds300f.
- 1 Shadow Boxer K spawns as the boss after 6.67 seconds200f.
- 1 Kid Tappa spawns after 3.33 seconds100f.
- When the base reaches 50% HP:
- 1 General GreGory spawns as the boss.
- When the base reaches 25% HP:
- 1 General GreGory spawns.
Strategy
Since Filibuster Obstructa will destroy the cat base in one hit regardless of where his attack fires off, you'll have to prevent him from even completing his 40-second attack animation.
Filibuster spawns with a Kid Tappa, which can be ignored, as he doesn't do much damage to the Cat Base. Due to how Long Distance works, you should not try to spawn any cat units until Filibuster is close enough to the base, as while his standing range is truly massive, his minimum range is only 300. Once enough money is accumulated, summon Awakened Bahamut along with other cats that are effective against Aliens. Don't focus on Wave Attackers, as he is immune to Wave Attacks (which means the Cat Cannon can't stop his attack), and don't bother with Warp Blockers, as none of the enemies here can warp. You can, however, use surge attackers (e.g. talented Dancer Cat), as while they are rare and tend to be inconsistent, Filibuster isn't immune to surges. Just beware that Filibuster usually won't move forward again once he's knocked back due to your units approaching him.
After dispatching Kid Tappa, several enemies will spawn one by one (due to the enemy limit) to assist Filibuster Obstructa, including Bun Bun Symbiote, Shadow Boxer K and a Bore. They largely function as meatshields for Filibuster Obstructa and players must build an effective multi-purpose lineup to deal with these threats before Filibuster launches his attack. Megaphrodite and Oni Hayabusa are excellent Uber Rares for this stage, while Butterfly Cat and Castaway Cat would be the most effective Super Rares. Once all these enemies are down Filibuster is no longer a threat due to his absurdly high KB count, and can be easily finished off, as with the General GreGories spawned on base hit.
Sniper the Cat is very effective against Filibuster Obstructa, as it's able to continuously interrupt its attacks, granted it doesn't hit the enemy in front.
Strategy 1
Lineup: Manic Mohawk Cat (30), Manic Eraser Cat (40), Eraser Cat (20+25), Can Can Cat (38+2), Fishman Cat (29+1), Octopus Cat (44+1), Seafarer Cat (29+1), iCat (30), Awakened Mina (30), Awakened Bahamut Cat (40)
Cat Cannon: Breakerblast or Thunderbolt
Kid Tappa spawns instantly, but just spawn Can Can Cat during this part and you won't need to do anything else until Kid Tappa is dead. Using the money from Kid Tappa's death, spawn Awakened Bahamut to charge into Filibuster to knock him back. The Shadow Boxer K will then come out, just meatshield to protect Bahamut and he will be able to kill it easily. The Bore is what iCat is for. Even though the iCats you spawn will probably not be able to reach the frontline in time, this is fine because Can Can will usually be able slow the Bore until iCat gets there and then Bahamut just goes ham. Once you have 2 desynced iCats, upgrade your Worker Cat during this part and don't spawn out anything more, as the Bore will die quickly due to Awakened Bahamut and since the Bore drops a lot of money upon death, upgrading your worker cat will allow you to get the most cash possible. Now for the hardest part of this battle; Bun Bun Symbiote. He is not really too big of a threat, as long as you have knockbacked Filibuster all the way to his base before hand, that is, because otherwise Awakened Mina will not be able to reach Filibuster and snipe him. Using the money that you got from the Bore, spawn out Awakened Mina, Fishman, Octopus and Seafarer. eventually Bun Bun Symbiote will go down, leaving 2 General GreGories to defend him, all of which are easily killed.
Trivia
- Prior to version 8.3.2, Filibuster Obstructa's LD effective area was 50~4,300, causing him to stand in front of Kid Tappa. Since the latter does negligible damage, this allowed players to cheese this stage by enabling Sniper The Cat and deploying no units until Filibuster Obstructa was defeated.