It's a slightly finicky Combat Training. And it stacks with Combat Training! If you're playing a deck that will play Attack events with some regularity, and that uses its ATK one or more times per turn, you'll get some solid value out of Fluid Motion.

You can also play it in multiples, if you're able to play multiple Attack events per turn. There's probably a Nova archetype where you try to get down multiple Fluid Motion, then go off with Unleash Nova Force and multiple cheap attacks (like the ones that come in his hero pack, conveniently) to get multiple basic attacks at an inflated ATK value.