With less than a week left until Battle for Azeroth launch, several achievements, mounts and items will become more difficult to obtain, and the Violet Spellwing mount will be removed from the game.
The Raid and Dungeon Meta Achievements from Legion are not being removed, however as focus switches to Battle for Azeroth, groups will be focusing on newer content and it may be harder to find groups for them for a while. These achievements will become easier in Battle for Azeroth, however some achievements will still need multiple players or not be soloable.
Hellfire Infernal and Shackled Ur'zul
The http://www.wowhead.com/item=137575/fiendish-hellfire-core from Mythic Gul'dan and http://www.wowhead.com/item=152789/shackled-urzul from Mythic Argus the Unmaker are both having their drop rates reduced to approximately 1% on the launch of Battle for Azeroth.
Fisherfriends of the Isles and Conjurer Margoss
The Fisherfriends of the Isles and http://www.wowhead.com/npc=108825/conjurer-margoss are fishing reputations and NPCs. The Fisherfriends are not being removed, however will become more difficult as less people will be making or joining fishing groups for older content as Battle for Azeroth releases. Each Fisherfriend rotates on a daily basis, and getting Best Friend with all Fisherfriends rewards http://wowhead.com/achievement=11725/fisherfriend-of-the-isles as well as the Hidden Appearances for the http://www.wowhead.com/item=133755/underlight-angler.
The http://www.wowhead.com/item=152901/kirin-tor-summoning-crystal, which summons the Violet Spellwing mount, will be made unobtainable on the release of Battle for Azeroth. The Violet Spellwing can simply be obtained from deafeating Heroic Argus the Unmaker.
Time is running out, and if you cannot afford to buy a carry then you should check the following Discord Communities for a chance at the mount:
Talons Vengeance is a PvP faction unlocked through one of the four quest lines for the Falcosaur mounts.http://www.wowhead.com/item=142363/mark-of-prey are the only way to get reputation with this faction. From Neutral to Honored, you must farm these off players at either PvP areas or Falcosaur world quest areas using http://www.wowhead.com/item=142361/ivory-talon. From Honored, you can buy http://www.wowhead.com/item=142367/ivory-feather, allowing you to get Marks of Prey in Battlegrounds. Due to less players being in Legion zones, this reputation will be a lot harder to get to Honored.
The Long Forgotten-Hippogryph is now harder to find because of Cross Realm Zone changes. As of pre-patch, the Broken Isles have been merged with other realms, meaning far less opportunities to find the crystals for this mount.
Check out the guide to Long-Forgotten Hippogryph to learn more about this mount.