Rakdos, Lord of Riots + Myr Retriever + Junk Diver + Phyrexian Altar

Rakdos, Lord of Riots

Myr Retriever

Junk Diver

Phyrexian Altar

How it works

1. Activate Phyrexian Altar by sacrificing Junk Diver, adding one mana of any color.
2. Junk Diver dies, returning Myr Retriever from your graveyard to your hand.
3. Cast Myr Retriever by paying 0.
4. Activate Phyrexian Altar by sacrificing Myr Retriever, adding one mana of any color.
5. Myr Retriever dies, returning Junk Diver from your graveyard to your hand.
6. Cast Junk Diver by paying at most 1.
7. Repeat.