In the spirit of automating away every shred of player skill this addon can disable abilities that will be ineffective if the target is immune (Immovable / Unstoppable) or if the target already has the effect (Stacks of 1-3). All so you don't accidentally use an ability that will have no effect and waste a GCD (global cooldown).
By default targeted abilities that Knock-down, Punt, Stagger, Silence or Disarm are configured accordingly.
To toggle the check for an ability SHIFT-LEFT CLICK the ability and a symbol will indicate its mode:
This example will block (grey out) Smashing Counter if target is Unstoppable, Repel Darkness if target is Immovable and Blazing Blade after 3 stacks.

Type /gcdsaver for settings.
Download: GCDsaver (v1.0.6)