Cutting Edge: Garrosh Hellscream (25 player)

These "Cutting Edge" achievements are Blizzards solution to raiders feeling like their accomplishments were cheapened when a few patches later, players could go in and easily defeat bosses that once caused hours of frustration. The only solace raiders previously has was "Check my achievement date, I got that so far before everyone," while now these provide a small reward for those who managed to clear content when it was current. In addition with 5.4 Blizzard has decided to add a distinction between 10 and 25 man kills.

So far we have six achievements, including this one:
Cutting Edge: Will of the Emperor
Cutting Edge: Grand Empress Shek'zeer
Cutting Edge: Sha of Fear
Cutting Edge: Lei Shen
Cutting Edge: Ra-den

And in 5.4 Blizzard will continue and expand on this pattern with both Cutting Edge: Garrosh Hellscream (25 player) and Cutting Edge: Garrosh Hellscream (10 player). By adding separate achievements for 10 and 25, Blizzard hopes to distinguish between the difficulties in both.

"Ahead of the Curve" achievements were added on top of the achievements introduced at the start of the expansion that were for heroic mode kills.
Ahead of the Curve: Will of the Emperor
Ahead of the Curve: Grand Empress Shek'zeer
Ahead of the Curve: Sha of Fear
Ahead of the Curve: Lei Shen

And, as said above, 5.4 Blizzard will continue and expand on this pattern with both Ahead of the Curve: Garrosh Hellscream (25 player) and Ahead of the Curve: Garrosh Hellscream (10 player). These normal mode achievements also award a mount. Please note that the 10 and 25 achieves award the same mount.

These achievements are phased out over time, becoming unattainable when the new raid tier is released. Meaning that after 5.4 the FoS for Lei Shen and Ra-Den will no longer be available.

Note that the titles are not linked to these achievements so if you didn't manage to get Delver of the Vaults, The Fearless, or Storm's End you can go back and get them later!

Asian server's have shorter lock outs than others and that's why no one considers them.

This kill, and hence, achievement, were first gained by Method (EU-Twisting Nether) on 1st of October 2013.

Many congratulations to them.