A channeled beam hits and petrifies the opponent. Additionally, the beam inflicts magic damage. If the opponent dies while Subjugation is active, the unfortunate soul will transform into a spectral companion of the Inquisitor.
With Regen per Hit on a weapon, the Inquisitor can recharge this CA immediately, allowing quick creation of many minions
If the Inquisitor is using the Doppelganger and doesn't want to get close to enemies, he can cast this CA on an enemy the Doppelganger is fighting. The enemy will be frozen in place, unable to fight back, suffering damage from both the magic beam and the Doppelganger, and when it dies it will join the Inquisitor as a minion. Repeat to quickly swell the ranks of followers.
Prior to the release of the Ice and Blood expansion, the Inquisitor could cast Inexorable Subjugation and then take other actions, such as movement, attack, or executing another combat art in a combo. In Ice and Blood this behavior became broken, and the Inquisitor became petrified for the duration of the spell, just like the enemy. This bug was fixed in the Community Patch 1.60.
Pros and Cons
The target enemy is frozen
Large number of followers can kill for the Inquisitor and create a buffer between him and enemies if desired
With Ice and Blood expansion, the Inquisitor can't move or attack while casting this spell (requires CM Patch to fix).
A single casting can rarely kill a champion on its own, so it will require softening them up with other attacks first