Karthus Q bug
I was playing an ARAM, and while in Death Defied, my Q had unlimited (as far as I could tell) range.
4 Comments
I recommend you attempt to recreate, and repost or let us know. I will also attempt this right now. (ARAM>KARTHAS>DEATH DEFIED>Q RANGE)
You should give all information that you can about the circumstances it occurred in if you don't know the cause yourself.
@Riot: End game items were 
.
it doesn't have unlimited range, it just LOOKS like it does. When in the passive and you Q outside of your range, the glyph in the middle of the Q stays at the max Q range, but it's the outline of the actual Q that looks like it has infinite range. Only you can see it, but it's rather irritating because it's also confusing. (P.S. it happens on SR as well)