Jace enters the battlefield with five loyalty counters due to Oath of Gideon and Lae'zel.
Activate Jace's third loyalty ability by removing five loyalty counters from it.
Jace dies as a state-based action due to having zero loyalty.
Resolve the Jace ability, creating two non-legendary copies of Jace, which enter with five loyalty counters each due to Oath of Gideon and Lae'zel.
Repeat from 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.