
I'd suggest this saying "non-Duration action" because things get difficult tracking-wise. Like if I Desert Throne a Desert Throne which then thrones a Wharf - how long does the first Desert Throne stay out?
Also it may be a bit strong with terminal draw. Desert Throne - Smithy is equivalent draw-wise to 3 Enchantresses, and only takes a single Action to play.
This card does nothing that we don't know yet from Ghost(ing a Duration): if you play Desert Throne in T1, it hits a Throne which thrones a Wharf in T2, then all 3 Actions are discarded at the end of T3.
Yeah, nothing new here. The throne room always stays out as long as the card it is used on.
That's why I think it is okay at

, because it delays the benefit to the next turn (for Desert Throne - Desert Throne even for an additional turn).
As comparison, also Throne Room - Smithy is a draw of 6 cards, but right now in your current turn and both cards are immediately back in your deck for the next use.
Speaking of tracking issues. I like the idea, to get an additional benefit for trashing your throne room like in Royal Hall, but tracking gets very hard if you use it on a duration card.
