You're allowed to use Buyback and you have to pay it separately.

A spell's "mana cost" is specifically the symbols printed in the upper right corner of the card. For Clockspinning, the mana cost would be . When an effect replaces a spell's mana cost with some alternative cost (or says you cast it "without paying its mana cost"), that's the only part of the total cost it's affecting. Any optional or mandatory additional costs that are also part of casting the spell (Buyback, Kicker, anything that says "as an additional cost to cast [this spell]", etc.) still need to be paid normally. In your example, casting Clockspinning with Buyback and help from As Foretold would cost a total of .

There won't be any "targeting issues". If the source of an ability on the stack goes away, it won't interfere with that ability resolving as normal unless it specifically depends on the source remaining on the battlefield, e.g. a "fight", a Banishing Light-like effect, or a specific restriction in the Oracle text like on Parallax Wave (for that last one, the printed text doesn't have it, you will need to look it up in Gatherer or some other similar reference to see the current errata).

To the first question: The extra beginning phase comes after the postcombat main phase. Since you're at the start of the postcombat main phase when the ability triggers, the words "this phase" are referring to that same postcombat main phase. The game will go to the end phase after the additional beginning phase is finished, so you won't be able to cast more "sorcery speed" spells unless you have something else going on (World at War is the only card I can think of that doesn't need help from some other effect like Vedalken Orrery, etc.).

To the second question: You won't get more saga triggers. Adding another lore counter to a saga is actually a turn-based action that happens as your precombat main phase begins. The reason the reminder text on sagas just says "after your draw step" is because reminder text is meant to be short and simple rather than 100% technically accurate.

To the main question: You won't be able to get around the restriction. The words "as a sorcery" or "at any time you could cast a sorcery" specifically mean "during a main phase on your turn when the stack is empty". No effect can change this definition.

To the side question: The "Activate only as a sorcery" at the end of Aurami's text box is part of the reminder text for encore. It's not part of Aurami's ability. You can activate Aurami's ability whenever, but unless you have something else going on that watches for cards in graveyards becoming targets, you'll only be able to do anything with the ability during your own turn.

For Elrond: Each token will trigger 3 times because of the 3 creatures entering the battlefield, for a total of 9. The check on how many times the trigger has resolved is part of the triggered ability itself, not a separate static ability of Elrond, so it will be applied even if Elrond isn't on the battlefield as it resolves. Each Elrond only tracks its own triggers, meaning you'll be tempted a total of 3 times, one from each Elrond.

For Inga: Inga's second ability triggers whenever she dies and then figures out the result later. Because it's not written in an "intervening 'if' clause" format ("When [event], if [condition], [effect]") that means it will still be put onto the stack even if 3 creatures haven't died yet. Even if it was written that way, you would still get the triggers in these examples because of everyone dying simultaneously due to the Legend Rule. You get to choose the order of all the ETB and dies triggers because they're all trying to go onto the stack at the same time, since the Legend Rule gets evaluated right before it's time to put the initial ETBs onto the stack. All the dies triggers will count at least 3 deaths in your examples and will give you cards.

To back up what wallisface is saying, here's the relevant rule about Sieges from the Comprehensive Rules document:

310.11b Sieges have the intrinsic ability “When the last defense counter is removed from this permanent, exile it, then you may cast it transformed without paying its mana cost.”

The specific interaction you describe doesn't work because Skull Skaab's ability says it only triggers for exploiting nontoken creatures. If you exploit 3 nontoken creatures instead then yes, you will get a total of 9 Skull Skaab triggers.

The Vessel's ability won't do anything in this situation. Created tokens don't come "from" anywhere, they're just created directly on the battlefield. If you were to use an effect that actually did exile the Vessel, create a copy of it and then specifically "cast" the copy then you would get what you want.

janitorstyle: An answer to your question has been up for a while. Since there don't seem to be any follow-ups or corrections that need to be made, I marked it as the "Accepted answer" so this topic can move out of the list of unanswered questions. In the future you can take care of this yourself using the "Mark as Answer" button on the response that you feel is the best answer to your question.

I try to avoid choosing my own responses when I do this, but in this case it was the only option.

Yes, copies of a merged permanent take all the merged characteristics, but let's get clear about the specifics of your example. A merged permanent starts with the characteristics of the top-most object and adds the abilities from everything below it. This means:

• If you put the Heron on top then you will have a 3/4 Elemental Bird named Dreamtail Heron with mana cost that has the Dreamtail Heron abilities plus the Mist-Syndicate Naga abilities
• If you put the Naga on top then you will have a 3/1 Naga Ninja named Mist-Syndicate Naga with mana cost that has the Naga abilities plus the Heron abilities

Yes, it will be able to ETB or attack. With the way the ability is written, returning an Elf to your hand isn't an additional cost to play or attack with the Elk. It's just part of the effect of that triggered ability. If you don't have any Elves in your graveyard when the Elk ETBs or attacks then the ability will trigger but then immediately get removed from the stack because there's no legal target for it.