To build a summoning station, build 4 pillars with 3 obsidian vertically each, adding a shroomlight on top. Spread these pillars out 3 blocks from each other. Then, add a respawn anchor in the middle. Summoning stations can summon 5 unique bosses depending on the item thrown on the respawn anchor. The following bosses a summoning station can summon are:
Ascalaphus - Glowstone (Block)