This idea is to make the melee system a little more complex and so, the gameplay more technical and skilled. It’s nothing new, but just a reworking of similar things already seen both in halo’s past and in other games. Three melee types:
B (normal): Classic melee.
3 Hits to kill, so B,B,B.
BB (quickly): Double melee.
You always need 3 hits to kill, but the first two are more fast so you can kill the enemy first (adding the thrid melee or an headshot). To perform it, you must press the B key twice very quickly. In game is not so easy to perform. The Double melee prevents the Holds also (read below).
B (kept pressed): Hold/assassination
Hold is an animation that kill the enemy, such as the assassination, but it’s performed in front of the opponent. It can be used after receiving a classic melee from the opponent, overturning the outcome of the duel.