I'll Pulverise You! is an achievement that requires the player to use the Pulverise ability on Masuta the Ascended in the Temple of Aminishi at the same time when he uses it. Both hits must land on the exact same tick.
This achievement unlocks as soon as it is completed; it does not require the player the kill Masuta the Ascended. It can be completed in story mode.
To get this achievement, run through a solo story mode dungeon up until Masuta the Ascended. Bring your best tank gear and a 2h weapon. Build to 100% adrenaline and then stall, not attacking the boss (if you get him down to 50% hp, he will phase and you will have to teleport out and try again). Unless he's using another special attack, stand right in front of him, or else your attacks will be delayed and timing will be harder. The tick after he says "I'll pulverise you", use pulverise. You should see matching animations of dragging your swords through the ground and the achievement will unlock.