Two of these psionic subclasses, the Psi Warrior (Fighter) and the Soulknife (Rogue), have a class feature called Psionic Power, that gives them Psionic Energy dice to fuel different powers.
Tasha’s Cauldron of Everything came out this week, heralding the introduction of the first official psionic subclasses into 5th Edition D&D! As such, the analysis below is wrong, but will be maintained for archival purposes.
