A: Intentionally taking an action that you know to be illegal, while seeking some advantage, will lead to some judges choosing to disqualify you. Your first example is clearly in that dangerous area, and I can’t say I’d disagree with a DQ in that case – assuming, that is, I can figure out what in the world you were hoping to gain from it.

The second example, if I read you correctly, asks if you can start to take an action and then – after gaining information – change your mind. Generating sufficient mana during the steps of casting a spell, but refusing to finish because you didn’t generate extra mana, is a very (dark) grey area, one I would not venture into, nor be very forgiving of.

So, to clearly state this: you can’t perform any of the listed examples!

Approved by Scott Marshall
Cards: Garruk’s Horde, Selvala, Explorer Returned, Force Spike, Chromatic Sphere

A: Yes! The Citadel has an alternate cost – it lets players cast a spell by paying life equal to the card’s converted mana cost instead of its normal cost. And the converted mana cost of a card with no mana cost (like Ancestral Vision) is zero. If the Vision is the top card of AP’s library, they’ll be able to cast it via the Citadel, and since its converted mana cost is zero, they’ll pay zero life to cast it.

Approved by Nathan Long

Cards: Bolas’s Citadel, Ancestral Vision

A: Assuming the creature AP targeted is one that they control (so that Feather’s ability triggers in the first place) and nothing else interferes, then yes, AP can return that card to their hand at the beginning of the next end step. The effects from both Feather, the Redeemed’s ability and Dreadhorde Arcanist’s ability each want to replace the action of putting the card into its owner’s graveyard with doing something else, so AP chooses one of those effects to apply (even though both effects want the card to end up in exile, they’re still separate effects). AP can choose to apply either effect–the other will then no longer apply and will do nothing. Choosing to apply Feather’s effect will create the delayed trigger that will return the card to their hand at the beginning of the next end step. (Choosing to apply the Arcanist’s effect instead would result in the card not returning, but nobody’s going to do that.)

Approved by Callum Milne  Cards: Feather, the Redeemed, Dreadhorde Arcanist