Lighting the Nether Keeper Altar and Awful Ghast Altar

Nether Keeper Altar

Place the Nether Keeper Altar block, then use the Igniter on it. The altar is the summoning point for the Nether Keeper Spawn Egg boss encounter. Surround the altar with Soul Bricks, Soul Bricks Slab, Soul Bricks Stairs, Soul Magma Bricks, and Soul Tiles to build a proper arena — those blocks are the mod's nether-themed building set and they fit the altar's palette. Keep Nether Bricks And Soul Sand, Nether Bricks And Soul Sand Slab, and Nether Bricks And Soul Sand Stairs on hand for detailing.

Awful Ghast Altar

Place the Awful Ghast Altar and light it the same way. It summons the Awful Ghast Spawn Egg encounter. Build the surrounding platform from Nether Bricks And Netherrack, Nether Bricks And Netherrack Slab, and Nether Bricks And Netherrack Stairs so the ghast has room to move and you have cover.

After the Fight

Both altars are one-shot spawners — you re-light them to re-summon. Bank the drops before you leave; the nether brick variants are also craftable via stonecutting, so you can rebuild the arena without hunting for more blocks.