In the new season, Aether Walker can remove the cooldown on Teleport. However, one player reflected that it still has ~0.5 sec cooldown, and asked for fix. Here, the community manager Tyvalir responded that the leaving a half-second is for safety net. Here is the original post:

"Although Aether Walker removes most of the cooldown on Teleport, it leaves a half-second "safety net.” This is because when we were testing the legendary power, we discovered a bug that caused people to double-teleport when they didn’t intend to do so, often putting them in harm’s way or costing them AP that they didn’t mean to spend.

While this means you won’t teleport quite as quickly as you would without a minor pause, the fix also prevents you from having to be very precise in how long you down the mouse button without wasting AP or putting you in danger.

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