This commercial jingle mashup by Grant Woolard was featured on the SMT blog a few weeks ago. I think it's super cute, and I'm going to take a little bit of time to talk about why it works.
First of all, the visual element is great. Each jingle is played on the piano with the product that it represents. Musically, each jingle is realtively simple, and most are in major keys. The simplicity is due to the fact that these tunes are meant to be easily remembered and re-singable. The point is for a company to create a sonic marker that quickly identifies their product. (For more on these sonic markers, see work by music theorist and all-around awesome dude, Alex Newton.)
What Woolard did to create this cover mashup was to piece together jingles and jingle fragments in counterpoint with one another to make functional sense. As a short example, I've transcribed a bit of the very beginning to show how it all goes together. This is the Old Spice jingle:
I've shown the implied harmonies underneath the staff. Here's the McDonald's jingle:
The identical harmonic implications are easy to see. Because of this, the two songs match up contrapuntally when played together. This is basically the way that the whole thing works: combining simple melodic ideas that fit together harmonically. Super cute, and illustrative of the way that short commercial jingles are structured.