Let's break down each option.
1. WindfallSo, I lied. You can't use
Windfall to get a better hand. Because of the
Spirit of the Labyrinth, everyone would discard their hands (10 damage to Mayael and Breya, 12 to Alesha) and then your opponents get 1 card, and you get none. You already drew a card this turn. Going into top-deck mode is a bad idea.
2. Chaos Warp the...Baneslayer AngelThis creature is not threatening. It may be the most powerful creature on the board, but that hardly matters. It isn't killing anyone any time soon. And although it doesn't matter much, Mayael is the most likely player to flip another powerful creature off of the top (more on this latter).
Shaman of Forgotten WaysThis card can end games, but not any time soon. Mayael missed a land drop, and the ability requires 11 mana. Don't worry about it.
Spirit of the LabyrinthYeah, this thing has to go. It pretty much disables Nekusar's strategy. But it doesn't necessarily have to go right away. You'll have 6 mana next turn, so you'll be able to use the
Chaos Warp, and then
Windfall.
Grand Architect/Pili-PalaWhile this combo is worrisome, you don't need to worry just yet.
Pili-Pala will enter with summoning sickness, and so can't use it's untap effect right away, so unless someone foolishly plays a haste enabler like
Concordant Crossroads or
Mass Hysteria, you have two turns to deal with this combo.
3. NekusarThis is the option that I would go for. Now is a good time to build up your board. It is highly unlikely that anyone will combo next turn. And on your next turn, you'll have 6 mana to get rid of the
Spirit of the Labyrinth, and then cast
Windfall. The following turn would be another wheel effect (
Runehorn Hellkite if nothing else) leading to massive life-loss for your opponents (2 for every card discarded, 1 for every card drawn). However, if Breya does play the
Pili-Pala, then the removal should (sadly) go that way.
Congratulations to Firegriff and Mustakotka.
A note on Chaos WarpOne of the biggest concerns I've seen from
Chaos Warp is the
fear that it will flip into something
really threatening. It can happen, but it's unlinkely. First off, a good chunk of most decks are lands, instants/sorceries, and mana ramp (let's assume about 60 to 70 cards). None of these are super threatening, so the majority of the time the card off the top is irrelevant.
The other factor is that you should be using
Chaos Warp on the real threats. It can hit any target so it's super versatile, and because it shuffles in the removed card is harder to recur. And just look at this last example. The two targets were
Spirit of the Labyrinth (a card that shuts down the game for you) and the
Pili-Pala combo (a game-winning combo). So long as you use
Chaos Warp in situations like this, it will
serve you well.