Add pixelated pets to your site in the form of funky animated retro space invaders.
Either install and activate the plugin via your WordPress Admin
Extract the zip file and just drop the contents in the wp-content/plugins/ directory of your WordPress installation and then activate the Plugin from Plugins page.
When first installed the Jellyfish Invaders plugin will show some invaders on every page of your blog. You can easily change this to your liking by visiting the setting page, you will find a link to the settings page in the Appearance menu of your WordPress admin.