Cera Sumat, Holy Avenger is a Legendary weapon obtainable from any mob (except Statues) with a 1:25000 drop chance.
Acts like a True-Melee sword, meaning that it doesn't release particles on swing, for example, like the Enchanted Sword does.
All attacks inflict the Curse of Light debuff for 5 seconds. This debuff makes enemies take 20% more damage from any damage source, and affected enemies deal 25% less damage to players.
It is a Legendary melee weapon, which means that its stats will grow with every boss killed, including some of the modded ones. Such as bosses from the Calamity mod.
Please note that killing a previously defeated boss will not upgrade the weapon. (Because it doesn't count as progress.)