Narset Vs. Monastery Siege

[MtJesus-Johnson]

I control {Narset, Enlightened Master. My opponent controls {Monastery Siege} choosing Dragons. Do I have to pay an additional 2 mana for the non creatures exiled with Narset?

Also, if my opponent were to have copied my Siege with his {Clever Impersonator}, would he even get to choose Khans or Dragons?

Thanks!

[Kaylesh]

{Narset, enlightened master}
You may cast non-creatures without paying their mana costs creates an alternate cost of {0}. If you target your opponent or his creatures while he controls {monastery siege} in dragons mode, you pay an additional {2}. So yes, you need to pay for your spells if they target your opponent or his permanents.

Edit: rulings on payment added below.

On the {clever impersonator}: it enters the battlefield as a copy of Siege, triggering the etb ability of Siege: choose Khans or Dragons.
Gatherer card ruling: 
20-9-2014   Any enters-the-battlefield abilities of the chosen permanent will trigger when Clever Impersonator enters the battlefield. Any "as [this permanent] enters the battlefield" or "[this permanent] enters the battlefield with" abilities of the chosen permanent will also work.

[Kaylesh]

117.8e: Some effects increase the cost to cast a spell or activate an ability without using the word "additional." Those are not additional costs, and are not considered until determining the total cost of a spell or ability as described in rule 601.2e.

117.8d: Additional costs don't change a spell's mana cost, only what its controller has to pay to cast it. Spells and abilities that ask for that spell's mana cost still see the original value.

601.2e: The player determines the total cost of the spell. Usually this is just the mana cost. Some spells have additional or alternative costs. Some effects may increase or reduce the cost to pay, or may provide other alternative costs. Costs may include paying mana, tapping permanents, sacrificing permanents, discarding cards, and so on. The total cost is the mana cost or alternative cost (as determined in rule 601.2b), plus all additional costs and cost increases, and minus all cost reductions. If the mana component of the total cost is reduced to nothing by cost reduction effects, it is considered to be {0}. It can't be reduced to less than {0}. Once the total cost is determined, any effects that directly affect the total cost are applied. Then the resulting total cost becomes "locked in." If effects would change the total cost after this time, they have no effect.

Edit: removed aura ruling as it does not apply in this case. Since you cast the aura spell from exile paying {0} it targets. If you were to blink it, it does not.

[MtJesus-Johnson]

Thanks a ton! 👍

[Kaylesh]

You wouldn't have to pay for those creatures. {monastery siege} ups the price of spells that "target you (the controller) or a permanent you control". The creatures you are playing do not target the Siege controller or his permanents, therefore do not incur the Siege tax.

I'm confused... OP asked about non-creatures exiled and cast with Narset's ability. Creatures exiled are just gone. However: creatures do not target, so would indeed not be taxed.

[Dsx Cherno]

Whoops. I thought it was creature spells exiled to the ability.