The Original

The lion and the unicorn

Were fighting for the crown

The lion beat the unicorn

All around the town.

Some gave them white bread,

And some gave them brown;

Some gave them plum cake

and drummed them out of town.

...and angerbda's way more badass version!

The Union and the Venusian

Were fighting for the Sun;

The Union ran the Venusian

All around Pluto.

Some cut through shipwrecks,

And some took a blow;

Some crashed on Ceres

And won the last touchdown. 

https://youtu.be/8pECGcSna4U