The devs have been looking to even the playing field where it relates to PvP as of late and changes have been aplenty. Many weapons and supers, as well as the way both buffs and nerfs are calculated, have been altered - but some items managed to slip through the cracks and so did various supers.
The One-Eyed mask was one of the exotics that remained untouched but the Crucible favorite is set for a nerf, with Bungie touching on plans for further balancing for the game in their most recent blog post. The mask, a titan helm, was specifically pointed to as one of the items that will undergo changes and, while players weren't told how exactly, they've been told to expect a difference when the next patch hits.
The mask has been around since the emergence of the Forsaken campaign and is favored by players who use Titans in Crucible matches. It's become quite popular as it allows Guardians to mark any opponent who causes damage to its wearer and grants them increased damage, full health, and an overshield if whoever's wearing can kill the marked attacker.
There's really no way to counter the effect and, although Bungie has tried to even things out by reducing the mark time and charging the health with the shield instead of earning it right away, it's still giving Titans too much of an advantage in PvP.
Striker Titans and Dawnblade Warlocks are now being targeted by Bungie's upcoming update. Bottom tree Striker Titans have been dominating PvP thanks to a super that lasts unreasonably long, as some players will have you know. And, despite a previous nerf, the complaints remain just about the same.
The developers are also looking to balance the Titan's Trample and Warlock's Everlasting Flames skills by implementing nerfs that reduce the super energy regeneration and lessen kill-based returns.