Ponysay

Add repository

$ sudo add-apt-repository ppa:vincent-c/ponysay

Change to an existing Ubuntu codename

Replace this

deb http://ppa.launchpad.net/vincent-c/ponysay/ubuntu yakkety main

With this

deb http://ppa.launchpad.net/vincent-c/ponysay/ubuntu xenial main

Install ponysay

$ sudo apt update
$ sudo apt install ponysay