Can you play Sun Disc and immediately exhaust it to make your next unit enter ready on the same turn?

Ruling: No. Sun Disc's exhaust ability has a [Legion] requirement, which means you must have played another card this turn for the ability to be active. Sun Disc itself does not count as "another card" for its own Legion requirement.

Sequence:

• Play a card (either before or after playing Sun Disc)
• Play Sun Disc (if you haven't already)
• Exhaust Sun Disc (Legion is now active because another card was played)
• Play your unit (it will enter ready)

Nuances:

• You need at least two cards played (one being Sun Disc, one being "another card") before exhausting Sun Disc for its ability to work.
• The exhaust ability can only be activated during your Main Phase when the game state is Open.