I thought there are systems out there. If you talk about arrows, then it'd be normal events with arrows responding, if you ever talk about letters W.S.D.... Then you talk about abilities.
Some pre-links :
3rd Person Camera movement
Complexe TopDown WASD Movement
Arrow Key Tutorial
First, you create 4 abilities ( Up - Down - Right - Left ), based on channel ( Change the string order and everything between each. Make them instant and visible. Remove all allowed targets. Then let's go to triggers :
NOTE : You should disable unit's movement speed to not go out of control. Set it to 0
Here is an example for moving around. (Remove Leaks yourself

)
Let's go to the jump :
Pre link :
Jump Tutorial MPI/MUI
Out-link Jump System
Okay, any jump needs a parabola maths formula, which I really, suck in it.
I won't give any example for it but of course just change the event of any of previous systems. It'll be smooth trust me
I made a 2D Parabola Jump System , if your map is 2-Dimensional I can send you my Sample Platformer map.
Greetings...