It seems that the Court of Oryx tier 3 boss changes on a weekly basis, and this week players have to deal with Thalnok, Fanatic of Crota.
Destiny ace Arekkz assures us that if you already beat Crota, this fight won't be too much of a challenge.
You need to make good use of the Relic in this mission to do maximum damage, although you need to watch out for his one-hit kills. You'll have four minutes to beat him.
Arekkz says that he'll continue to produce guides as new Tier 3 bosses appear, so if you're a Destiny fanatic it's worth subscribing to his channel.