Library of Leng is an interesting card for this as well. All you need is a discard outlet.
But the rulings on Library of Leng are tricky, I'm getting clarification in the rulings section for help on this.
But I assume you can use things like Merfolk Looter to discard your spell to the top of library.
It will for Looter. It will not work on something like Stronghold Machinist or Mind Over Matter, though, because those are costs. It also won't work if something says "you may discard a card". Subjunctive makes it optional. Same thing if your opponent uses Painful Quandary or Torment of Hailfire: The fact that you can choose another option means the effect isn't forcing you.
Card advantage is not the same thing as card draw. Something for 2B cannot be strictly worse than something for BBB or 3BB. If you're taking out Swords to Plowshares for Plummet, you're a fool. Stop doing these things!
It will for Looter. It will not work on something like Stronghold Machinist or Mind Over Matter, though, because those are costs. It also won't work if something says "you may discard a card". Subjunctive makes it optional. Same thing if your opponent uses Painful Quandary or Torment of Hailfire: The fact that you can choose another option means the effect isn't forcing you.
If we're looting, Thought Reflection and Alhammarret's Archive.
On phasing: