Fiora's Ultimate...
There is almost a 50/50 chance of it not proccing the healing part of her ultimate. Generally, if I ult someone and it's been on them for roughly 3+ seconds, it's guaranteed to work, but any shorter and it won't. I've put it on someone within half a second before they even die, I've put it on them and auto attacked one of the vitals, then Q'd the other which killed them, but it happened so fast, my ult still doesn't proc the heal. It's extremely irritating...