A Freeware arena Shoot 'Em Up that centers around user-made content. The game comes with an editor that lets you make your own enemies, then lets you blow them to bits.It comprises of two modes: Free Play, which pits you against one or more of the available enemies and Try, which gives the player different scenarios. The latter is not as popular, due to the fact that it's harder to make scenarios than enemies.Available Here, with more bosses available here.
Bullet Hell: There is a play mode called "danmaku", which reduces your hitbox to 1 pixel. And a ship type that's called, yes, Bullet Hell: very little health, pretty fast, and requires special energy to fire Blaster weapons.
Bullfight Boss: Mini Core. Turns to face you. Charges. Repeats those steps until destroyed.
The Big Core part also does this as well, only it's much slower.
Fake Difficulty: The use of the Screen (blur) effector looped just to confuse the player is one example.
Fan Fic: Some of the more prevalent boss makers out there like to put together stories to go with their bosses. Eboshidori is one (his "Mara" series is finished and on YouTube), as is A70M1C (the "][nfector" series).
Getting your boss ][nfected is actually a very great honor for you as a boss creator.
Follow the Leader: Eboshidori pretty much singlehandedly invented the "What If...?" scenarios, the Search-Light wings, custom player weapons and the very, very often used "Globe of light spewing bullets" type of boss. And many, many creations with borrowed ideas followed. Eboshidori is to Fraxy, is what Simpsons are to animated sitcoms.
Game-Breaking Bug: Several bosses don't work properly in the latest beta versions, despite appearing fine in the editor. These include Eboshidori's Virupaksa II and Sakra-Devanam(This one recently began working again, however). Oneshiningstar's CX-07: Giant Delta 3 has its 3rd delta self-destruct for no apparent reason just before the 4th phase begins. However, if it was not so, you'd be panicking. That thing is spam.
Glass Cannon: The new (as of version 20090706) Quicker type. Its attack is insane, its initial boost is insane, its regeneration is just as insane, but its slow and lacks hit points.
Initial Burst: Practically every bullet-type weapon can be this.
Spray Burst: The hardest to make of the three, but sometimes present.
Exploding Shot: Energy Egg/Missile.
Trick Boss: The Clock Trap, which starts out as a harmless, unprotected core until you find out that was a holding mechanisim for a robotic laser blender that you'd be crazy to take on. Luckily, it's also defeated by managing to escape it's gravitational pull and the surrounding laser emitters on top of being dedicated enough to destroy it's core.
Up to Eleven: "Death Label" Bosses, which are harder versions of other bosses.
Wave Motion Gun: The Laser. Bonus points for being available in three different sizes.
Mind Screw: Zarro Tsu 's latest boss Wrath especilly during the final phase against White where it seems like reality itself is breaing down.
Oh Crap: The ending of Mara's battle with Phantom 30-K results in Phantom 30-K freaking out and calling for help, then getting blown out of space.
One-Winged Angel: The Fraxy community loves this trope, as many bosses utilize this.
A Famous Example is A70M1C's Osiris, which seems to be a mechanical thing before transforming into an Energy Being for a long battle.
Atomic Vault 99, which turns out to be holding The Avatar, Osiris's first form. However, on Hard Mode, it spectacularly transforms into Osiris for an extremely long battle.
Eboshidori recently created one for the Final Boss of his Fan Fic Fragments of Men, Samsara. After nearly depleting his life bar, he merges with a crucifix, then attemps to fly to the top of the screen. If you don't beat him before then, he, cross and all, transform into his angelic Sunyata form, which rains even more Bullet Hell down on you than before. Admittedly, fighting him like that is a lot better than just beating his temporary Clipped Wing Angel form, but still...
Serial Escalation: Eboshidori created a boss called Matrix Hibachi, which was pretty hard. Shortly after, he gave us the "Death Label" version, which had bullet patterns similar to the original, only harder. To clarify, the original was already Bullet Hell.
Zarro Tsu, in what seems to be a complete "Screw You" to the player, released the "Death Label" version of his A.N.G.E.L. Boss. This is regarded as a completely evil move because....well, see Death Is a Slap on the Wrist.
Sinister Geometry: Oomagatuhi's DANMAKU-DAMASII-Mk5 as well as Eboshidori's True Acala and the second form of Broken Dream.