Summon Herobrine through a ritual you have to defend, then beat him in a three-phase boss fight you win by learning his moves.
His first phase. Sword in one hand, pickaxe in the other.
Four soul braziers, a circle of runes and a storm that keeps putting them out.
The rite only moves forward while the braziers burn.
In the last stage a rift opens over the altar.
Right after the rite ends.
The line of light shows where he's going. Step off it.
Jump it or sidestep it. Blocks stop it.
He's slow while he spins, and dizzy for a moment after.
It rolls outward from him. Jump it.
It turns slower than you can run around him, and blocks stop it.
Only the real one's eyes glow.
The circle stops following you just before he lands. That's when you move.
His last phase. Everything gets faster.
Before you ever summon him, he's out there watching.
Enhanced Sword, Herobrine's Pickaxe and the Builder's Crown.