I have a slideshow on my page and I want to know
1 is it possible to add video to the slideshow? I’m guessing I have to animated gif it.
2 is it possible to randomize the images? as in when a repeat viewer comes to the site they don’t always see the exact same order of images.
Welcome onboard @bobbosfunhouse! 
The Image Gallery is specifically for images. You can place an animated gif but it won’t animate in Preview.
It is also not possible to randomise images at this stage to present a different image to last time a User viewed your Image Gallery.
The Sparkle Team are always looking for feedback and suggestions so that could be next?..