This champion uses Flow. She builds up flow as she moves, generating 1 flow every 1 unit traveled, up to 600. If Miriam stops moving for more than 1 second, or changes direction drastically, all flow is lost.
A "drastic" change in direction counts as facing a direction outside of a 45° cone in front of you in under .5 seconds.
This cone is displayed by faint lines. The cones center will point in the direction you were facing .5 seconds ago so that you can plot your direction accordingly.
Agile catch is my least favorite ability. It doesn't fit the kit or theme. Suggestions?
Theoretical Item Build
Noxian cyrcus or something... blah blah... murder.... Signature move was leaping from a tight rope and tossing daggers around a person to hit a target behind them.
flow is the name of the game. The most difficulty comes with plotting your paths so that you can utilize Readied strike and Signature Leap. You need to run in predictable paths in order to use these, however you can use them in any direction once you have the required flow.
When you engage, the cooldown of Signature Leap will go up. Make sure you want to go in as giving and taking damage can prevent you from escaping.
You need open ground to leap, make sure you plot your paths correctly.
Tips to counter
If she flips over a wall, stop chasing. She will get away unless you have equal mobility or long range cc.
If you can surprise her, you can likely kill her, as she will be unlikely to escape long enough to use her Signature Leap.
Watch her flow bar as it will tell you when she is about to harass (or engage after level 6). She needs to move in almost a line in order to charge it up.