Using an illusion needed Mental Energy. Stronger Mental Energy meant stronger illusion. World Energy was just a determining factor on how much skill you could cast and how long were you able to use illusion continuously.
To make an analogy, World Energy served as a 'fuel' while the other kind of energy such as Mental Energy, Spiritual Energy, etc. were the 'car, yacht, helicopter, etc.' On the other hand, the person containing both energies was the 'driver'.
The more fuel you had, the longer you could last. The better car, the more efficient would it be. And as the driver was good enough, so as the desired effects.
But Jim's situation was different. He didn't need Mental Energy to use illusion. He had no Mental Energy after all. He had no car!
