Sharkrons are Hardmodeenemies fired by Duke Fishron's Sharknado attack. They travel in an arc, descending at a slower speed after reaching maximum height. They are killed instantly upon impact with blocks.
Notes
Due to their high defense rating, trying to kill Sharkrons with low-damage weapons (less than 50 damage per hit) can prove difficult, as your attacks will be reduced to 1 damage, or 2 on critical hits.
Homing weapons may target Sharkrons instead of Duke Fishron, which is usually undesirable.
Trivia
According to the Bestiary, they are the offspring of Duke Fishron himself, despite having barely any of the same physical features.
The Cthulhunado may be a reference to Cthulhu being “The father of all sharks.”
Their name is a combination of Shark, and the suffix -ron, a pattern shared by several bosses, enemies, & items, including Skeletron, Duke Fishron, the Pigron, Fishotron and Skeletron Prime.
The Bestiary entry for the Sharkron: "Duke Fishron's nature as a form of chimera causes his offspring to emerge more shark-like, which he uses as minions in battle."