Tyranitar A -> A-
This mon has suffered a lot in the last six months, in part because of Ferro/Clef cores that can eat its attacks, in part because of EQ M-Latios and Megazam, in part because of Steelium Heatran, in part because Zygarde's now one of the best mons in the game, in part because of Hippowdon. That's all in addition to long relevant threats like Ash Gren, Protean Gren (now with Low Kick or Z-Dig), Kartana, and Landorus-T continuing to make it hard for Tyranitar to fit into the meta. Its speed tier is straight up garbage - it doesn't beat offense, it doesn't break stall, it doesn't really trap anything outside of Lele or other choiced mons. Other less common sets like Scarftar and AV Tar are fine but they really don't do much to ease Tyranitar's tendency to get walled and U-Turn chipped by Landorus and without the Choice Band Tar can no longer break mons like Clefable who will stall it out of Stone Edge PP in a heartbeat if given the chance.
While it has a great dual STAB and is capable of denting lotws of mons with CB equipped, its lack of recovery, bad speed tier, and the increased irrelevance of some of the things its supposed to check (Blace, Latios without EQ, Zapdos, etc.) has made it difficult to justify picking Tyranitar for a team. It's lack of recovery and weakess to all hazards is bad, its matchup against ladder offense (usually consisting of Gren/Lando/Gyara/Zygarde) is bad outside of Blacephalon, and its prospects seem to just get worse with each new meta development. New niche arrivals like Suicune and Serperior further mess up its flow as they can set up and PP stall it or fish for a Stone Edge miss. Honestly, A- might even be too high for it at this point.
Celesteela A -> A+
Probably a bit of a controversial nom but I think this thing's performance on stall, balance, and bulky offense is worthy of a rank increase. As one of the tier's best answers to M-Latios/M-Zam (with a more SpDef spread), I have trouble finding ways to keep it on the bench, particularly because it checks Protean Gren, Lele, M-Diancie, Landorus-T, Kartana, M-Scizor, Ferrothorn, Clefable, and Bulu. It checks most Scarfers, mons that rely on HJK, EQ spam, or Steel stabs (e.g. Exca) and it loves leeching Heatran/Zapdos and stacking residual damage against them and its other checks. Leech stall is great for wasting Heatran or Ash Gren's PP as well. Magnezone is still a threat, but can be played around in some cases (not to mention you can Flamethrower/EQ it on the switch if yer good). Obviously Zygarde is a real threat against Steela if it comes in for free, but the same is true of other highly-viable walls like Ferro and Pex. Overall this mon has become way better than it used to be as a balance core member and I think it deserves a shout out because of that.
Mage A+ -> S
This just shouldn't happen, Mage is a great mon that can sweep certain teams but can't break Ferro/Pex cores very well and needs team support. AV sets are ok but they don't really check anything except for Lele/Zam (who again can get by them). Other changes to the meta like Zygarde, Hippow, and SD Bulu make Mage a worse pick than it used to be. Its matchup against Heatran and Landorus is particularly bad.
Ash Gren A+ -> S
Probably nah on this one too, Ash Gren is amazing and threatening and I use it all the time. But I don't see it being Heatran/Lando tier any more than Kartana, Lele, or Koko - the other 3 mons in A+ who you absolutely have to be prepared for or else you lose to them. Everything about Ash-Gren is great, though it falters against stall and needs help getting into play without taking 50% damage. Definitely a great pick, but not on Lando/Heatran's level right now, imo.