I think latest idea was to do Grail Sacrament this very turn. Because we need to pay Mareinette price after it. Ironically Spoiled is not fast enough. Biedde for sure can capture somepony and then guard them.
And there is also that hopeful possibility of Lantern 3 Celestia taking a good look at Mareinette and going all "Face the Sun, Monster." It is even more likely to happen if she is pretending to be Cadance at the time considering Celestia's previous experience with a shapeshifter(we know she isn't but Celestia is working on limited information) on the throne.
Putting aside that I just don't like Mareinette or her Grail Sacrament, or really any emotional arguments at all, my problem with it mechanically is that we do not actually have reason to consider that it's possible at all. Bird never actually said that he would allow such as thing, just more-or-less that he would think about it if enough people were willing for go for the Grail Sacrament generally.
this is quite tempting as far asbriberyhumble requests go, but... well, why don't we get the thread to a point they are willing to commit to this first? Then we can discuss terms
Or we deal with Celestia instead. I already argued at some point that to safely clear All-in we need to resolve her issue. I don't even care that much how exactly as long as Luna is okay with it or accepts it as necessary. But the moment she and Luna begin seriously fighting they will obliterate Canterlot with their no holds barred attacks. And Luna is necessary for All-in expedition. This is most narratively compelling moment for their confrontation if we don't do something before that.
Some Sacraments can, it depends on the Sacrament itself. The more important thing is that Bird has confirmed that generally, unless whatever missing part of a Sacrament can be fulfilled by an on-command thing like scraps from a Name or (presumably) our Leash, all of the requirements for a Sacrament must be fulfilled by turn start before the Sacrament action may be taken. We cannot do either the Grail or Moth Sacrament this turn, because we have not fulfilled the conditions for either (Moth 4 4/4 + Confidant that we're willing to sacrifice for Moth, a Minion we're willing to sacrifice or a Prisoner for Grail). The only reason we should be able to sort of cheat this in regards to the Grail Sacrament is because Mareinette's binding renewal technically happens "between" turns but has the Grail Sacrament as an available option, so if we successfully acquire a prisoner this turn, that means there should be a prisoner available during the contract renewal and therefore for the Grail Sacrament.
I agree with your strategy/point of view, but our true enemy here isn't exactly Celestia, it is Daybreaker.
Technically you are correct but they are in the same body so we still would need to target Celestia. And while we need to wait because Luna asked for it, and there is still hope for some mental solution the moment it looks like we can't outpace her with our Moth all bets are off. If we need to knock her out, or develop ritual to put her to sleep so we can exchange her for principal Celestia human Twilight's way then so be it. Let Harmony sort them out.