Resolve + Inspiration as Rell Runes
Aftershock is Rell’s best and most commonly selected keystone. The rune bulks you up, increasing both armour and magic resistance, whenever you immobilize a champion. Aftershock will activate, so you will always be tankier when you choose to initiate a fight.
On the Inspiration tree, you can pick up Cosmic Insight to help with your cooldowns, as well as Hextech Flashtraption. Having an extra way to close the gap with the Flashtraption will make an engage much easier to pull off.