The Alien variant of Teacher Bun Bun has very high health and very high attack power. He is a bit harder to defeat than the other Bun Bun variants, due to him having half as many knockbacks. Even worse, he has a 5% chance to create a Level 1 Shockwave. Luckily, the Shockwave comes out rarely; in other words, Bun Bun Symbiote doesn't make a Shockwave most of the time.
While the Shockwave is rare, it can destroy your meatshields and long-range attackers due to Bun Bun Symbiote's high attack power.
Even though he can only create a Level 1 Shockwave, this still greatly increases his range, killing all of your Dragons, Ururun, and Bahamut and possibly knocking back any Uber Rares that you may have.
Another good option is God-Emperor Sodom because of his resistance to floating.
Sadako Cat is sometimes considered the "anti-Bun Bun" because Sadako resists Bun Bun's attacks and can weaken Bun Bun's power. Octopus Cat, Sadako Cat's True Form, is considered the anti-Bun Bun Symbiote. On top of performance upgrades, Octopus can neutralize Shockwaves, making Bun Bun Symbiote's occasional Wave attacks only affect Meatshields. Very useful in later instances of this enemy.
The abbreviation for Bun Bun Symbiote is BBS, which is an acronym meaning Bulletin Board System, a method of communication through the internet. Coincidentally, BBS's school apparently now has a hive mind.