One sneak teleports you onto the last player you hit. The mark stays valid for 15 seconds, the teleport recharges in 10 seconds.
The Ninja is the server's pursuit kit. An opponent who breaks off on one heart does not get away: you mark him, you let him go, you catch him.
But you have no mobility beyond that. No speed, no dash, no jump. Between two teleports you run like everyone else — and if your target leaves your range or the 15 seconds run out, the mark drops and you are in the open.