Due to the exposure of the excessive Psionic energies from prolonged contact with mindflayers, you have gained the ability to project mental hallucinations with the minor illusion cantrip. However, the cost of this exposure has resulted in a second split personality which can manifest itself when the user casts any version of disguise self spell.
When you cast the disguise self spell, roll your current Psionic die. On a roll of 1 you take on the form and personality of your alternate personality, regardless of what you wanted to disguise as. This personality is rather unstable in some way or another and has several character flaws (Examples could be: refuses to acknowledge other party members exist, doesn’t wear clothing, addiction to substances...). You retain your recent memories and abilities but act according to this split personality.
If you have no Psionic die when casting disguise self, meaning your mental energies are sapped you will flip a coin rather than roll a dice. If the coin flip is Heads then you take on the split personality. The less Psionic energy you have the harder it is to hold off this personality.
This feat does not alter the size of your Psionic dice.