Rundvelt Hordemaster + Mortuary + Phyrexian Altar

Rundvelt Hordemaster

Mortuary

Phyrexian Altar

How it works

1. Activate Phyrexian Altar by sacrificing a Goblin that can be cast using one colored mana, adding one mana of any color.
2. The Goblin dies, triggering Rundvelt Hordemaster and Mortuary.
3. Resolve the Mortuary trigger, putting the Goblin on top of your library from your graveyard.
4. Resolve the Rundvelt Hordemaster trigger, exiling the Goblin and allowing you to cast it until the end of your next turn.
5. Cast the Goblin from exile by paying its mana cost.
6. Repeat.