Knockback

When something damages you and you have no immunity, your velocity is overwritten rather than adjusted: roughly 18 miles per hour upward and 23 away from the source. Because it replaces your current speed instead of adding to it, a single hit can cancel a jump outright or fling you off a platform you were standing still on.

Which way counts as away depends on the side of your own hitbox that got hit, not on where the attacker is or which direction it was travelling. A laser fired from your right can shove you to the right if it connected on your left side. Ogre club swings are the loud exception to all of this: they hit far harder than anything else and they still move you even through full immunity.

Chained knockback is how most deaths actually happen. Two things break the loop. Firing a hook grants immunity for as long as you stay attached, which makes it the panic button in a corridor. Failing that, ride the push rather than fighting it: falling back down through the knockback drops you into range for another two or three hits, and forcing your way sideways through an enemy needs serious movement speed, of the kind a Panic Necklace provides after you have already been hurt.

Permanent immunity is cheap and worth taking early. The Cobalt Shield line covers it from mid pre-Hardmode onward, every later shield in that chain keeps the property, and a full Gladiator set grants it too, so there is rarely a reason to fight without it.

On the other side of the exchange, the weapon's base value is first reduced by the target's knockback resistance, then multiplied by 1.1 if the target is burning with Cursed Inferno, then capped, then multiplied by 1.4 on a critical strike. The cap is 16, or 22.4 through a critical strike, and it is applied after resistance rather than before.

You can raise your own output with modifiers, the Titan Glove chain, a Titan Potion, the Celestial Shell family, and the Shroomite or Vortex stealth effects. Given the cap, that is only worth doing on weapons whose base value is low enough to still have headroom.

This is the part no tooltip mentions. The game compares your hit against the target's maximum health, counting the random roll, defense and critical doubling. Clear a tenth of its health in Classic, or a fifteenth in Expert and above, and the hit counts as strong: double the knockback value is added to the target's horizontal speed, up to a ceiling. Come in under that line and the target's speed is instead set to the knockback value scaled by its resistance a second time, so resistance is counted twice on weak hits.

The practical result is that knockback quietly stops working as you progress. Enemy health pools grow faster than your per-hit damage, the fraction shrinks, and a weapon that used to pin things against a wall starts nudging them. It is also why knockback collapses in multiplayer: enemy health scales with player count, so hits that used to clear the threshold no longer do.

Vertical knockback follows the same split and is then scaled down, halved for floating enemies and cut to three quarters for everything else. Snow Flinx get an extra multiplier on strong hits specifically, which is why they launch further than anything of their size should.

A melee swing always throws the target the way you are facing, regardless of where on the enemy the hit landed. Most projectiles throw it in the direction the projectile was travelling, not away from the point of contact. A handful push away from you instead, which is what makes sword beams like Excalibur's behave symmetrically when enemies are pressing in from both sides.

Almost every boss and most boss minions are immune, along with everything that burrows through blocks and nearly all rooted plants. The Brain of Cthulhu and its Creepers are the notable exceptions, though in Expert multiplayer their resistance climbs steeply with each extra player until it is effectively total. Some enemies switch state instead of being immune outright: biome Mimics can be pushed while grounded and cannot while they are in the air for any reason.

Beyond that, the immune list is mostly heavy hitters and set pieces: the Paladin, the Headless Horseman, Martian walkers, Blazing Wheels, the Dungeon Guardian.

The Slap Hand carries the highest printed value in the game, with the jousting lance family close behind, and lances also scale with how fast you are moving, so a mount at full speed pushes harder than the number implies. A Thorns Potion retaliates with a respectable shove of its own.

The genuine outlier is the Gray Zapinator and Orange Zapinator. Each beam has a small chance to multiply its own knockback by nine on a hit, and the multiplier compounds across successive hits from the same beam. Chaining it far enough to produce an eight figure value is somewhere around a one in a billion event, but the code allows it.