Variants
Sharkron spawns as 2 variants that share one bestiary entry; each row is one variant's exact stats.
where they come from
Sharkrons exist only inside the Duke Fishron fight. His tornado attacks are the spawner: each funnel holds a few of them for a moment before firing them out at wherever you happen to be. Nothing in the open world produces one, so you will never meet them anywhere else.
reading and surviving them
The pause inside the funnel is your warning. Once one launches it commits to a fixed arc, so the dodge is decided the instant it leaves, and the arc slows as it falls, which makes the back half of the path much easier to read than the opening burst. Blocks kill them instantly, so a fight arena with a platform layer above you erases a good share of every volley before it arrives.
They are armored past what light weapons can chip, so shooting at them is usually just uptime stolen from the boss. Dodge instead. The one loadout trap is homing damage, which happily locks onto a passing Sharkron and leaves the Duke alone, and that alone is a reason to bring something you aim yourself to this fight.