The Meowmere is a Hardmode, post-Moon Lord, autoswingingmelee weapon. When swung, it fires a projectile trailed by a rainbow and shaped like a cat's head, and consumes no mana or ammunition. The projectile is affected by gravity, pierces multiple enemies, and ricochets off of blocks. Each ricochet emits an explosion that damages nearby enemies. The projectile disappears after piercing four enemies (hitting the fifth one) or after ricocheting four times (hitting a block for the fifth time). The Meowmere has a 11.11*1/9 (11.11%) chance to be dropped by the Moon Lord.
The cat projectile makes a "meow" sound and produces a small rainbow explosion every time it ricochets. This explosion deals damage to all enemies within a 3×3-tile rectangle centered on the point of impact, and grows by half a tile each ricochet, up to a 5×5-tile rectangle on the final explosion.
The cat projectile travels at 61 mph.
It can be very useful in close-range situations, for instance inside the Hardmode post-Plantera Dungeon. The bouncing projectiles with area-of-effect damage are highly effective against the large crowds of enemies in small chambers.
The cat projectiles can be reflected by enemies like the Selenian. Care should be taken around those enemies, especially at close range.
If the player is annoyed by the Meowmere's sound, they can alter the game's sound files to remove or change it: The relevant files are Item_57.xnb and Item_58.xnb in the sounds folder (<Steam folder>\steamapps\common\Terraria\Content\Sounds). They can be deleted or alternatively be replaced with copies of Item_8.xnb, a hardly noticeable sound.
The cat-shaped rainbow projectiles are inspired by the Nyan Cat meme.
The Meowmere has the highest listed base damage of all weapons in the game, apart from explosives. However, other endgame weapons like the Zenith, Terrarian, or Star Wrath often have much higher DPS, e.g. due to unlisted bonuses.
It was referred to as Meowmur before its release.
In the Mobile version, the developers changed the game credits on April Fools' Day to mention a supposed new melee weapon that would shoot cat projectiles, referring to the Meowmere.