Cosmic runes in Dungeoneering are used to cast various Magic spells. They can be crafted from rune essence or obtained as a drop from various monsters. 1 type of rune or arrow can be bound to the ammo slot, holding up to 125 (or 225 after completing Salt in the Wound) runes. Cosmic runes are not a recommended bind for players who have completed the medium Daemonheim Tasks, as 40 cosmic and law runes are provided at the start of each floor.
Cosmic runes can be crafted with rune essence at an altar on complexity 3+ dungeons by players with at least level 27 Runecrafting. Each action can use up to 5 essence, with each essence giving more runes based on your Runecrafting level. Make-X in Dungeoneering allows up to 50 actions to be performed, allowing a maximum of 250 essence used. Each crafting action grants 0.8 experience.