Perhaps Ningibalahaaahalahasahgh Hydra at Grauberg? I don't know how much of a bitch he is at 99 (All Abyssea content seems pretty easy since I've started soloing on THF for my seals), but he was a pain in the ass at 90.
Edit: Solo Alfard and tank from the front.
Both hydras are soloable at 99 with evasion setup, tanking from wherever stops it from doing nerve gas(I forget). Just takes forever.
That's why they're saying from the front, which is when Nerve Gas can go off instead of just Serpentine Tail.
Which would make it basically impossible. If you did manage to win that way, it would just require an insane amount of luck on dodging/para not proccing, so I'm not sure what the point would be?
Self-imposed restrictions, aside from not using a brew, are lame imo.
Three. I count three wooshes.
Tinnin:
I actually did a series of solo's on the whole ZNM path for informational purpose/fun:
Tinnin Path
Sarameya Path
Tyger Path
Got another old content soloing itch:
Ouryu
Add-On Shantotto EXP final fight:
Other project I haven't finished yet, SCNM:
La Value NMs:
---Boss Fight BCNM
Beadeaux NMs:
Castle O. NMs:
Bahamut version 2 solo: