Mashup videos are all over the place. The quality ranges from superb to dismal. YouTube is full of sources. Since most take images from there anyway, try to pick more than just a few. How to make a good mashup video:
Use clips from a variety of sources.
Have a unifying theme; make it make sense.
As always, use creative editing well timed with the music.
Do not make a video of any of these personal themes:
Your great summer vacation.
Walking around some fascinating city.
Having fun in your back yard.
Your friends and family will love seeing these, but most people will find them kinda boring. Actually, between you and me, your friends and family will pretend to be interested, but they won’t like them either.