Knockdown

Knockdown is part of TERA's combat system. Knocked down monster or player can not use any skills, attack or defense themself until they rise up.

All classes gain special skill Retaliate that only activates when in knocked down state, which allows jump up, hurting enemies around. Retaliate has significant cooldown, which means it's not available if knocked down again right away. This allows certain classes (like Berserker) to take opponents to knockdown-lock by repeatedly knocking them down in PvP.

In TERA character who gets knocked down also turns 180 decrees around. This is most likely relic from old PVP. Character who gets knocked down is not taking extra damage from back hits.

Risk of getting knocked down depends on your Balance Factor. Generally classes wearing cloth armor have lowest Balance, and classes with Metal Armor and tanks (includes Warrior tank in Defensive Stance) highest.

There are certain skills that improve your balance or make you impossible to be knocked down. Priest is immune to knockdowns while casting Purifying Circle, slayer with Knockdown Strike, Whirlwind or Heart Thrust, sorcerer while casting Nova. Humans have also special race specific activated skill to reduce chance of knockdown in PVP.

Furthermore priest's Arise skill raises all knocked down allies and gives them a buff that doubles balance for few seconds. Also almost all shield skills prevent knockdown while shield lasts.

Jumping lowers your balance significantly and most attacks will result knockdown while jumping. This can be used if you want to intentionally get knocked down by group of mobs for farming retaliate achievement. This can also be done in PVP to avoid stunning attack and convert stun to knockdown you can escape with retaliate. However, this is considered bad manners in duels.

Certain Achievements are gained by knocking down enemies, like And Stay Down! by knocking down Mutated Kaidun in Necromancer Tomb, or getting knocked down, like Prone to Violence for killing monsters with retaliate. Dungeon bosses cannot generally be knocked down. There are exceptions, like Mutated Kaidun for achievement. There's text on screen when Kaidun is hurt and he can be knocked down.