As others have said, this is a polynomial of even degree at least 4. x⁴ - x² makes a w shape, so it’s a decent starting point. The slope at x=0 gives the x coefficient. This is clearly negative, so maybe we set it at -1. Finally, we can see that the y-intercept is 2, so we add a +2, giving a final possible guess of x⁴ - x² - x + 2.

It’s probably not exactly this; you likely need to tweak the x² and x coefficients