With the 6.22 stealth changes, a new "Shimmer" effect has been added. When you manage to damage a stealthed champion (invis or camouflage) with an ability, a brief image of them will appear - please note that this does not REVEAL it simply shows an outline of the champion.
(filmed on the 10/21 PBE build.)
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This is idea for Critical Strike version of Youmuu's Ghostblade originally was crits based but...