Sylas and Ekko
Thinking about Sylas taking the ults of everybody is actually makes sense, but what about Ekko. If the logic takes place and Sylas take Ekko's ultimate to return back in time, he will back until the moment before he took his ultimate and stop there because he won't have the ability to return anymore. In the situation of Sylas taking the ultimate and using it at the same moment, he wont move at all...so it makes kind of problem.