Augmented for Outsider, 18 Days, and DC. Will 23. Will be using until it works. Slightly more likely then Crystallise.
I think I'll try rolling the saves to save time, here's the first 20. Hooray for small PP regeneration.
Assuming Pit Fiend: PR 32 | Will +21 (If it has any bonus to Will, then only 1's work. If not 1-2)
Spoiler: Rolls
Show
PR: (1d20+18)[37] | Will (1d20+21)[33]
PR: (1d20+18)[35] | Will (1d20+21)[28]
PR: (1d20+18)[33] | Will (1d20+21)[22]
PR: (1d20+18)[29] | Will (1d20+21)[30]
PR: (1d20+18)[32] | Will (1d20+21)[26]
PR: (1d20+18)[35] | Will (1d20+21)[37]
PR: (1d20+18)[23] | Will (1d20+21)[33]
PR: (1d20+18)[26] | Will (1d20+21)[35]
PR: (1d20+18)[34] | Will (1d20+21)[26]
PR: (1d20+18)[32] | Will (1d20+21)[35]
PR: (1d20+18)[38] | Will (1d20+21)[29]
PR: (1d20+18)[22] | Will (1d20+21)[40]
PR: (1d20+18)[34] | Will (1d20+21)[36]
PR: (1d20+18)[23] | Will (1d20+21)[31]
PR: (1d20+18)[24] | Will (1d20+21)[34]
PR: (1d20+18)[32] | Will (1d20+21)[26]
PR: (1d20+18)[22] | Will (1d20+21)[32]
PR: (1d20+18)[29] | Will (1d20+21)[40]
PR: (1d20+18)[29] | Will (1d20+21)[22]
PR: (1d20+18)[26] | Will (1d20+21)[26]
Sigh... any other ideas?