The Reins of the Plagued Proto-Drake is a Proto-drake mount. Along with the [Reins of the Black Proto-Drake], it was a reward for the Naxxramas Meta-achievements before being removed after the introduction of Ulduar. This mount can be purchased through the Black Market Auction House.
Here you can buy The Reins of the Plagued Proto-Drake for EU or US Servers.
You'll get guide for getting The Reins of the Plagued Proto-Drake
You'll be able to get Plagued Proto-Drake
Plagued Proto-Drake mount
Additional budget for Character transfer or Character boost to max level. BMAH Services in Shadowlands now requirement to have a max level character on server, so Trial character will not work.
Free time on evening, if you choose selfplay option