MTG Salvation

E, nothing! C is also true.

War's Toll creates a requirement – "they all go in if able" – while Silent Arbiter creates a restriction – "only one." You must meet every restriction while maximizing the number of requirements, and that number is zero. No other creatures are able to attack, so they don't. You meet the same number of requirements whether you attack with one guy or none, so either is okay. Attacking with all breaks the restriction, so no.

C, if it doesn't matter, do whatever!

Judges got sick of having to police graveyard order being changed while digging for relevant cards when there were no cards that cared about the order. So now you're allowed to shuffle around your graveyard to put cards with flashback on top, literally shuffle it to choose a random card, and so on. But Legacy and Vintage tournaments can't do that because we're hardcore like that and don't need to rearrange our graveyards to figure out what we have.

B, C, and D! Maybe E, but who knows!

"Any time you could cast an instant" doesn't mean that you could literally cast an instant right then; otherwise, you'd have to show that you have an instant in hand to cast, and then it's just getting stupid. LED has a mana ability, so it'll work here. Dryad Arbor has flash, and the rules you can't break about lands without explicit permission are "one per turn" and "only your turn." You can break the normal timing rules if something gives you an additional permission, which Teferi does. Triggers are entirely unaffected by split second, so that's all well and good. But you can only suspend a card when you could literally cast it, unlike the "could cast an instant" timing thing, so you can't suspend Ancestral Visions in response to anything.

D, copy something new!

Leaves-the-battlefield triggers look back in time, and at that time, the Metamorph had persist so it can trigger. Copy effects do not copy counters on an object, so the Metamorph can still persist. Once it does, though, it will have no memory of what it once was, and won't be a Primus anymore; you'll have to copy something new and get your -1/-1 counter on it.

You should know that I am very pro-zombie, so shame on you if you answered E.

C and E, stuff!

But only if you cast True Conviction second, otherwise they're all false! TRAP!

Assuming you did cast True Conviction second here. B can't be true because your guys don't have trample. They won't hit him after they're blocked. C is true because of timestamps – they'll gain double strike after losing all abilities. Because of this, E is also true, as they have lifelink. But D isn't, since they'll kill the blockers with first-strike damage, gaining you only one.

C, 2 to the face!

Fireball has its damage divided evenly, so your opponent won't be doing any division as it's announced. The damage is divided upon resolution among legal targets. Since you're the only legal target, you're going to take 2 damage.

D, a blob!

You know how they keep saying that only copy effects get copied? This is one of the two very rare exceptions. Being face down creates a set of copiable values, so that's what gets copied, and you get a face-up 2/2 blob of nothing creature.

The one final exception is stuff like Primal Clay, in case it gets Mirrorweaved instead of Cloned. Those enter-the-battlefield replacements that define characteristics are also copiable.

B, no Maze for you!

Unfair exchanges are indeed possible, as the Plotter's flavor text tells you, but one-sided exchanges aren't. If you're ever trying to exchange X for Y (and the actual word "exchange" has to be used here), but this is impossible for any reason, including X or y not being around anymore, then the deal's off.

E, then B and D at once,then maybe A!

C is right out, since the end step is its own step before the cleanup step. First, the active player discards down to seven. After that, B and D happen simultaneously for reasons lost to the mists of time. Then if there are any state-based actions or triggers begging for attention like sticky toddlers, the active player gets priority to deal with them.

A

This one's pretty standard: illegal cards in deck become basic lands. Yes, this makes his deck entirely unplayable. Yes, that is very unfortunate, and the organizer should probably refund him when he inevitably drops. But he's not disqualified, no matter how poor his deck ends up, and he can't just remake his deck at a Competitive event.

A, B, and D

Drafts where you don't keep the cards are fine, as long as that's announced in advance. It even produces some better play sometimes, since people don't care about card value! Drafts are also legal with any mix of product, no matter how silly, as long as everyone gets the same product and it's all sealed. Extended and Block became valid FNM formats a couple months ago, yay! Modern won't be sanctionable for stores until late 2011 or early 2012, so you can't do that yet. (But who says you need to sanction an event to have a good time?) Grand Melee remains unsanctionable since it is a silly, crazy format. (And very often not a good time.) And you cannot sanction your own Pro Tour. Can't imagine why not.

F, your opponent's fine!

The guy who jumped in and started babbling is the one who provided outside assistance, so he's the one who'll get a Match Loss for the infraction. But your opponent? What did he do? He didn't ask for help. If this was a big conspiracy set up before the event, then he did and there's a bigger issue, but the judge will figure that out later and we'll assume that's not the case here.

"Player Communication Violation" means something very specific, not "anything about communication." You have to unknowingly incorrectly state or fail to state something that you are required to be truthful about for it to be a PCV.

This is also not a Game Rule Violation, since there's no game rule your opponent broke.

The real answer is actually G, but if everyone knew about the DCI's sonic program, we might have to kill you.

N, D, µ, A, E, B, C

And that's leaving out things like J, H, and 3 that don't really make sense in the context of the question. Those may appear anywhere in the process depending on how observant you are.

Remember that all crazy teenagers have tried magic pills. Adamaro's stats change as soon as the card leaves your hand, and the Witches doesn't trigger until you've finished paying for Swat, so it won't resolve till later. Other than that, the article I linked explains the steps of casting a spell just fine, despite being kind of old.