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I want to create a reminder used in arena, when the healer of enemy team got CCed. So i can do CC chain or cross CC immediately.

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In side the trigger, unit type and a new option called "enemy smart group", which support filter of specs. healer, dps, tank.

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not come in mind yet

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There is a "arena" unit for your use case

Specifically they want the role filter for the Arena unit type.
The info is in the API (AFAIK) but it can't be done the same way as with group members, so requires some specific handling.