Attention: Strikethrough users (Akali, Fizz, Yasuo)
I don't know if this is intentional, but when you dash as either Akali, Fizz or Yasuo to a target, and there is no space behind the target (i.e. terrain) to strikethrough, it enforces some 'minimum dash time' to complete the dash.
Normal dashes, like Irelia's or Xin Zhao's don't have this problem because their dashes lands them directly on top of the target so there is no chance for them to be 'pushed' into terrian - the dash time is based directly on how much they travelled during the dash from start to end point, according to their missile speed.
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Pick Fizz or Yasuo, and dash in melee range through a minion, given there is space to strikethrough. Then repeat this at a camp on one of the jungle monsters, making sure there is no space behind the jungle monster to strikethrough.
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For Akali, its a bit different, since she only strikes through a much smaller distance. Pick Akali and dash at max range to a minion, given there is space to strikethrough. Then repeat this at a camp on one of the jungle monsters, making sure there is no space behind the jungle monster to strikethrough.
As you can see, for strikethrough users, if there is space to complete the strikethrough behind the target, then the dash missile speed of the champion remains intact. However, when there is no space behind the target to strikethrough, the dash missile speed of the champion 'decreases' and slows down the the dash completion time.
So unlike a normal dash, which just finishes early since it lands the dashing champion on top of the target from start point, a strikethrough user will slow down and take the same overall amount of time to complete the dash + strikethrough distance even through there is no space to travel.
Logically, this shouldn't happen. The strikethrough user should just finish the dash early at the point where it cannot strikethrough any further instead of just locking them out of any player input, slowing down their dash missile speed and making them feel sluggish/clunky.
So, beware of walls/terrain where there is no space to strikethrough. It can cause additional delay which can potentially cost you a fight.