If you've been wondering why you haven't seen 
Tooth Fairy or 
Forged By The Master in a while: they're not just rare, they're gone. Across ~365k ARAM: Mayhem games, 12 augments stopped showing up mid-day on October 21, the day 26.21 went live, and none of them have come back in 26.22.
What the data shows
- In the first ~9 hours of 26.21, these 12 augments were still being picked.
- The last pick of any of them was at 16:58 UTC on October 21.
- The game client build didn't change at that point, so this looks like a server-side disable (hotfix), not a patch.
- The game files still list all 12 as enabled, even in 26.22. So if you're going by the client data, they'd look like they're still in the pool.
The 12 disabled augments
| Augment | Rarity |
|---|---|
| Forged By The Master | Silver |
| Tooth Fairy | Gold |
 Endless Decimation | Gold |
 Snowblast | Gold |
 Shark Tempest | Gold |
 Nature is Healing | Gold |
 Pat On The Back | Gold |
 Shark Bait | Gold |
 Hellbent | Prismatic |
 Surge Field | Prismatic |
 Squishy Slappy Grab | Prismatic |
 Spirit Bomb | Prismatic |
None of this has been mentioned in any patch notes. Which is kind of hilarious, because the 26.22 patch notes do include a buff to Squishy Slappy Grab, an augment that's currently not in the game.
Data: ~365k ARAM: Mayhem games from 26.21 and 26.22.