"D Rank Stones: Poor Mega Stones. Stones in this rank have only specific recipients and will fail if used on anything else."
Abomasite
Alakazite
May I ask what the specific recipients are? There aren't any on the viability rankings, so I'm assuming there aren't really any decent recipients that wouldn't prefer another stone 9 times out of 10. In which case the description is kinda misleading, and just trying to make the useless stones feel better.
But if of course there are decent users, I wanna know so that I can be "that guy" and use them.
EDIT: Also I believe Pidgeotite is misspelled in the Mega Stone Viability Rankings.
Slower Ice-types should generally be usable with Abomasite if you want to use Hail. Problem is that most have mediocre stats and typing in general, but here are a few possibilities.
65 / 60 / 110 / 130 / 95 / 65 -> 65 / 100 / 130 / 170 / 125 / 35
Glaceon basically gets really strong and quite good bulk, but it can't really do much besides spamming Blizzard. I guess it could run Substitute / Blizzard / Baton Pass / Hidden Power Ground | Shadow Ball, but it seems mediocre even if its stats are good.
50 / 65 / 107 / 105 / 107 / 86 -> 50 / 105 / 127 / 145 / 137 / 56
Rotom-Frost gets a reliable STAB move for the first time in its life, and can spam Blizzard as much as it wants now, but its speed has been cut badly. Volt Switch is still nice for momentum though, and Electric STAB pairs well with the Ice-STAB. As the last move you could use something like Will-o-Wisp to support the team. Overall not very good, but looks viable.
110 / 80 / 90 / 95 / 90 / 65 -> 110 / 120 / 110 / 135 / 120 / 35
Walrein's stats become pretty amazing as it becomes incredibly bulky, though the Water/Ice type hinders it a lot. As the others it can now spam Blizzard, together with its Water STAB, while this is more bulky and has a better type than the other too. The lack of recovery sucks though, as do the SR weakness and the fact that it's really slow.
Other than these, Vanilluxe could work with a mixed set (Rock Polish / Blizzard / Explosion / Hidden Power Ground), it seems really niche but is the only thing that can really abuse both boosts and the hail. Otherwise it could be used for mixed wallbreakers which don't care about their speed stats too much. Although most will still take damage from hail, it may just help them break through walls so I guess that could be viable on some stuff. Kyurem also becomes quite monstrous with this stone with 170 mixed offensive stats, so that could be a good recipient too for wallbreaking, I just wanted to cover some more unknown things. But in general, the fact this stone mostly benefits the Ice-typing and the fact that there are so few good Ice-types really hinders it. I'd like to hear it if anyone finds a viable set on a non-Ice type though.
As for Alakazite, it seems pretty much outclassed to me. The only saving grace could be if you really want Trace, but most of the time you'll want one of the other stones instead. It gives a nice +40 boosts in Special Attack and +30 in Speed, but multiple stones seem to do that, with most having better abilities and +100 instead of +90. Although, I'd like to see it if anyone feels Trace can be useful. (Maybe it can be good against some stones, it seems quite bad against -ate's tbh)