Emperor's Dais

Lot's of people have been talking about Emperor's Dias:

It is worded exactly like Diana, Lunari.

Therefore:

When you conquer here: Trigger condition

you may: Option to put the trigger on the chain or not

pay [1] and return a unit you control here to its owner's hand.: Effect 1. Must target the unit on finalization

If you do, play a 2 [Might] Sand Soldier unit token here. Effect 2

429.3. only says that plays "can" activate Add abilities but does not require them to do so. If they do not pay [1] because they lack the Energy to do so, they will not execute the "If you do" sections of Diana and Dias.

That being said if you have 1 floating in your rune pool, the effect will just consume that as part of the effect.

So you are able to decline to pay the 1 (unless it's floating in your rune pool). Still bounce your unit, but you will -not- create a Sand Soldier.