Heroes 5.5 WarGame Edition - Tactical Edition.

I understand that the problem isn't that the unit is uncontrollable. The problem is that the Crystal isn't considered a creature. And the function that tracks a unit's death relies on the CREATURE designation. Although, I might be wrong.

I'm more interested in whether it's possible to activate the Sentinel not only on melee attacks against the target, but also on ranged attacks and spells.