The dominant term is -2x⁴.
As X approaches infinite, y is naturally going to be really large as well.
Remember that a number with an even exponent, regardless of whether it's positive or negative, will be positive.
As x approaches infinite, y will approach -2 * ∞, or -∞. Therefore, the end behavior in the positive direction is y=-∞
As x approaches negative infinite, y will approach -2 *∞ again. This is because -∞⁴ = ∞. Therefore, the end behavior in the negative direction is also y=-∞
Basically, due to the dominance of the -2x^4 term, the function will look more or less like a downward facing parabola with a y-intercept of 3.