There are many ways to create a reflective floor in Adobe Illustrator. My way of doing it consist of 6 easy steps : 
‍
1.Select the object and then copy (ctrl C) and paste it on the same

position (ctrl F).

2.Open the transform panel

3.click the Rectangle tool to create a rectangle of the object just flipped

over.

4.Open the gradient panel to set the desired proportions of the gradient in

the object.

5.Select the object open the Transparency panel and then select the

"Make Opacity Mask"command

6.Click to edit opacity mask and then click the gradient tool adjust the

image to your liking.

That's all. Now you can use it on you portfolio mockup to make it look professional.
You're welcome :)