If I use Entei's "Flare Fall" attack but I only have 3 Basic Fire Energy in play, will my one Prism Energy count and let me do damage?
Yes, that works (as long as Prism Energy is attached to a Basic Pokemon). Flare Fall does not specifically say the energy has to be Basic Energy.
Source: Ascending Heroes FAQ; TPCi Rules Team (2026-01-22)

Relevant cards

Note: All applicable cards may not be listed below.
ME25_25
ME25_25
ME25_216
ME25_216