To fulfil a prophecy: What is Eldritch Blast's maximum range? The range I care about is between the Tiefling and the max-distance target at the time of the Tiefling making their attack.
Assuming the following constraints:
- The allowed material is the PHB, DMG, MM, EE, SCAG, XGtE, VGtM, MToF, AC, and the SA Compendium v2.3 and the errata linked therein.
- The setting is the Forgotten Realms, 1492 DR.
- The character is level 20 and conforms to PC rules.
- The character is allowed to multiclass and may indulge in optional rules.
- The character is a Tiefling.
- The character has access to up to 5 major magic items and up to 20 minor magic items (XGtE 135), but not to artefacts.
- The process has to exclude Wish and Gate whether cast by a magic item or not.
- The process has to be reliable (at least 95% of times once during a long rest or more consistently) and reproducible.
- The character is without allies at the start of the process but may create or conjure allies. The Tiefling knows no friendly creature and currently has no familiar.
- The whole set-up has to be prepared within 10 rounds, and Eldritch Blast has to be cast on the 11th round on the turn of the Tiefling, completing the process.