Looking at the trailer, you can see many hint.
First, he has the ability to reverse time. I believe this is his ultimate. He reverse time 4 times in the trailer, so I believe it's has a very short cooldown like Kass ultimate. But, as Kass ultimate, cost more when he recast.
If you notice, there is an animation that he pulls his chains link to his machine. I believe that is a part of his kit - to trigger a moment to reverse time. But I don't think it is a part of his ultimate. If he activate the ultimate first to actually reverse time, this would the enemy team react, making the ultimate useless. But then, he still need something to trigger it, frequently. I believe that is his passive, a passive that triggered at the beginning of a team fight. You can also see that he doesn't healed from this ability. And the ability seems to affect everything around him (the candle at the beginning and the collapse wall at the end of the trailer).
OK next. He seems to be a very mobility champion. He has a dash, which seems to be a double dash (0:44). He has a swing, which seems to be a double swing (1:36). But he seems to not using the reactivations everytime. If you notice, the double-ability is the first ability used after he pulls the chain. Do you think what I'm thinking? Here is my thought.
Passive: Every 15/12/9 second, his next basic ability doesn't be on cooldown. He can reactivate the spell just as he hasn't use it the second before. The moment the passive triggered is considered Locked Moment, stayed for 5 second. During this time, he can use his ultimate to reverse back to Locked Moment. He can reactivate the spell up to 4 times, the more he reactivate, the more the cost is (100/150/200/250 mana). As he reverse time, the ability to double cast is consider unused, enable for the next basic ability cast within 5 second.
I think this can actually his passive, as it really fit with his ultimate. He has the ability to outcome his enemy as he can cast more spell than him (in the trailer, he at least use it 3 times!!!)
I'm working on the kit. See ya later.
With this kit, I can't decide Ekko second role as a Mage or an Assasin :|. His burst during ultimate is quite good and his target can't really escape from him.
- This ability surely has low cooldown. He used it 1:43 but can use it again 1:49 so the cooldown is around 4-8 second.
- Condition: Locked Moment is triggered.