Craft it
You need
Make it at (any of these)
Needs a Pal with Handiwork. Best:Solenne (Lv 8), Selyne (Lv 7), Wistella (Lv 6)
Work: 10,000
[Tides of Terraria]
A seal inscribed with cryptic symbols.
Offer to a Summoning Altar to summon a powerful entity.
You need
Make it at (any of these)
Needs a Pal with Handiwork. Best:Solenne (Lv 8), Selyne (Lv 7), Wistella (Lv 6)
Work: 10,000
Keep one of these schematics in your Inventory or in a chest at your base to unlock crafting Celestial Sigil at that tier and rarity.