Boss Skills

Directly from my guide (which is still growing), I've decided to bold the more typical boss skills you might encounter.

Bosses have the following attacks and skills:

• Dispel. The sudden and inexplicable disappearance of buffs usually indicates that you've been Dispelled. Watch those buffs! This is usually a Magician's worst nightmare since Magic Guard is usually the only thing preventing their deaths. As a Warrior however, you should be okay. Dispel does not nullify potion-like effects, including Onyx Apples and GM's Bless. Dispel does not dismiss player summons, such as Beholder and Bahamut.
• Seal, Darkness, Weaken, Curse. You're more likely to have learned what they do if you've run into spellcaster monsters before. If you don't know, Seal prevents usage of active skills, Darkness reduces your hit-rate to roughly 25%, Weaken disables jumping, and Curse halves your experience gains.
• Stunning. Try to ride out the duration if you can, since there's no way to undo this infliction.
• Slow. An allcure does not remove this infliction, but a Priest/Bishop's Dispel skill can. Using a mount or the skill Rush can override, but not undo, this skill. I would advise caution when using a mount however. Other players cannot tell if you're Slowed or not.
• Heal. Active healing recovers tens of thousands of HP.
• An attack that damages your MP instead of your HP.
• An attack that does enough damage to bring your MP, then your HP, down to 1 each. This is officially known as the "Deadly Attack", but amongst the player population, it's dubbed the "1/1 attack". The 1/1 attack is highly lethal, but never fatal. In other words, the 1/1 attack cannot kill you directly.
• A variant of the monster wDef and mDef buffs, the wAtk Null and mAtk Null. It's unofficially known much better as the "super wDef/mDef". This buff reduces any damage you do down to 1 per hit (3 if you use Meso Explosion; this is most likely a glitch). Sacrifice (Dragon Knight skill) does not work against wAtk Null.
• Monster summoning. The monsters summoned are usually unique to the boss, and they might carry their own surprises. Infamous "boss spawns" are bombs, which are incredibly deadly. Pianus's Blood Boom summons can do up to 11,000 damage!
• Super Knock Back attacks that send you sailing across the map. King Sage Cat's Super KB is rather pathetic, but it still sends you skidding across the ground.
• Seduce. VERY DEADLY! While seduced, you randomly jump or go left or right, but never a combination of the three (thus if you're on a rope, you don't go anywhere). You also cannot do ANYTHING while seduced, with the exception of chat, Hero's Will, and game functions. Or Alt+F4 if you're really desperate. Seduce skills are generally limited by how many players it can affect.

NOTES: Attacks that do damage and status inflictions at the same time have to be able to hit you, or they don't work. Status infliction skills that don't do damage can hit you regardless, as long as you are within range. Sometimes a regular monster may have a skill listed above, such as Typhons having Super KB or Sharks having Dispel.

Yeah, I'm sorta a freak xD

To be fair and technical though, there could be an unlimited number of monster skills, such as Bodyguard B's attack that reduces your HP down to 1, but brings your MP up to max.