The Black Dire Riding Squirrel is up temporarily on the RIFT Store Feature Page (main page) for the next 2 days until 12pm PST on 27th Jan 2015.
Black Dire Riding Squirrel Mount
The Black Dire Riding Squirrel costs 3,000 Credits (2,700 for Patrons). It matches your fastest mount and is applied account-wide.
It used to only be available via rare chance from Limited Edition: Regulos’ Trove lockboxes that cost 700 Credits each so this is a rare opportunity to get it with a fixed amount of Credits.
It is also giftable if you go into RIFT Store -> Mounts -> Premium. So you could potentially find a gifter willing to trade for plat (or a nice Essence)
RiftGrate 
they should make it permanent on rift store and any idea what that costume set is?
The helm is the Helm of the Demon Lord, which is only available via codes Trion have handed out in events/contests.
The rest of the outfit is from the “Freelancer’s Plate Bundle” on RIFT Store -> Wardrobe. You can also buy each piece from Tempest Bay pvp vendors for Favor (pvp currency). It’s the Warrior’s Freelancer set. “Mercenary Petrikov” sells each piece at /setywaypoint 12994 11704 in Tempest Bay.