This is just a simple guid to killing any boss in terraria (Including skelly prime)
First you will need;
1 stack of hellstone
Full cobalt or mythrill armour
Crystal storm/ Cursed Flames
About 3 mega Healing potions
1 stack of Mega Mana Potions
And about 40-60 Def
Second Things you must NOT have;
All of the obby items mess up the plan!
Okay! Now to set it up make a long bridge of hellstone, and wait till night time!
Once night has come, spawn your boss and stay on the bridge, so the thing is with this is that the hellstone does damage to you, and the cross necless makes it so you can't take sdamage for seconds so that means the boss can't hurt you unless you step off the hellstone so just rapid fire on them and within 3-8 minutes you will have you souls!