Disappearing Skeletron

[Vincent]

Anyone else have Skeletron disappearing, mid-fight? I've been trying to figure out a strategy to kill him and lately have tried to use a slime mount to drag him into the sky, while using a featherfall potion, and chucking a bunch of projectiles in his face on the way back down, speeding up my fall to dodge his hands. Unfortunately, he seems to despawn whenever you get too far away from him, even if you are directly above his spawn point. The range at which he seems to despawn seems to be entirely random, as I've seen it happen while his hands are on my screen. It's incredibly frustrating to spend potions/food on a fight that ends because of a ♥♥♥♥-ty game mechanic. Why the hell is this a thing?

[Danté]

he despawns at daylight, and just kill him with a weapon, use vile thorn, worked like a charm for me.

[Flyingbox]

It's considered fleeing. Don't run away.
It's not a mechanic, it's to prevent a glaring exploit of running faster than the boss and shooting it harmlessly.

[Tealtyr]

Mobs despawn if they are far enough offscreen. Bosses are no different from normal enemies.

[Vincent]

Probably should have mentioned, I'm playing on expert, so the standard fare used to kill him on normal doesn't work, at 400 health and molten armor he'll kill you in a matter of seconds if you can't get away from him, and destroying one of his hands grants him an additional, and very powerful, ability to fire homing projectiles. He also seems to move a lot faster than I remember him being in normal. Also, I'm well aware that when dawn comes, he instakills you and despawns, wasn't referring to that. Thirdly, comparing fleeing from normal enemies to bosses is pointless, the entire point of a boss fight is consistantly staying out of their line of fire while sustaining damage on them, which why he moves so insanely fast, and why he kills you at daybreak if you take too long. Living in constant fear of him despawning if you do this too well is asinine.

[⭕⃤ ᠌ Vooverine]

i'm having the exact same thing happen to me. I've been playing with a couple of my mates on expert and we've been trying to kill skeletron for ages. It always seems to disappear, sometimes right in front of me, and some other times it would just float away into the sky....