Debuff

Block Active Skills

The Block Active Skills debuff prevents a Champion from using any of their active skills, other than their default skill. A Champion under a Block Active Skills debuff will still have their cooldowns reduced as normal.
What the game's own status effects screen says

In the game data this effect appears as BlockActiveSkills.

Champions that apply it

55 champions have a skill that applies Block Active Skills, according to the effect lines in the game data. This lists who applies it, not how reliably: chance, duration and resistance are on each champion's page.

The description is the game's own text. It has not been tested in battle here, and the game's wording can be loose (for example about numbers that differ between versions of an effect). See Data quality for what has and has not been checked. Found a mistake? Use "Report a problem" at the bottom of the page.