Hello, @Evolution
I know 2 ways: using velocity and using timers+move by
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My velocity behaviors had a bug when character stops if you touched 2 buttons at same time and then released only one, but this can be easily fixed with «Behaviors on/off»
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Simply timer and move by.. Behaviors on/off required for proper work without any glitches.
P.S. It's hard to see behavior off connections on this screenshot (sorry, my butterfingers), but it's simple: turn off right timer when character moves left and turn off left timer when character moves right.
I can send the project by e-mail if ya want.
Hope this helps! :-)