Solidifier

King Slime always leaves one behind, so there is no drop rate to worry about and no reason to fight him twice for it. That makes it one of the very few crafting stations you can guarantee in the first hours of a world, assuming you can find or summon him.

Most of what it makes is decoration: the slime block furniture line, some lighting, and a few odd conversions including a route to hardened sand and sandstone. The two entries that matter in a fight are the slime spear and the slime whip, which hand a summoner an early weapon at the cost of nothing more exotic than gel.

Skyblock worlds start with one already sitting on the island, where it is the only crafting station you have until you build the rest.