Jace enters the battlefield with six loyalty counters due to Doubling Season.
Activate Jace's third loyalty ability by removing five loyalty counters from it, creating two nonlegendary copies of Jace that enter the battlefield with six loyalty counters each due to Doubling Season.
Repeat step 3 using a Jace token.
Once you have infinite Jace tokens, you may activate their second loyalty abilities by removing two loyalty counters from them, creating infinite 2/2 Illusion creature tokens.