give renekton a slow with empowered e

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His E gives 35% armor reduction dude. That's no joke. That's better than Wukong's Q. It's as much as a Black Cleaver full stack.

I'd put the slow on his ultimate. Like: 1% slow per 2% rage currently on Renekton.

Renekton doesn't need or want to use his empowered E often in lane, but it is already a MASSIVELY strong ability past laning. It's an AoE massive armor reduction for 4 seconds: that's stronger than quite a lot of skills. Giving it a slow makes it a great ability to use EVERYTIME and removes a lot of the choices Renekton has to make (Empowered Q for more healing, or W for more damage and stun, or E for armor reduction) in favor of "use E because it is the best".