Urza, Prince of Kroog + Myr Battlesphere + Ashnod's Altar
Urza, Prince of Kroog
Myr Battlesphere
Ashnod's Altar
Infinite colorless manaInfinite copies of artifacts you controlInfinite creature tokensInfinite death triggersInfinite creature ETBInfinite creature LTBInfinite creature sacrifice triggersInfinite creature copies of artifacts you control
How it works
Activate Urza by paying 6, creating a token copy of Myr Battlesphere that is a 1/1 Soldier in addition to its other types.
The Myr Battlesphere token enters the battlefield, creating four 1/1 Myr artifact creature tokens.
Activate Ashnod's Altar three times by sacrificing three Myr tokens, adding six C.
Repeat.
Once you have infinite mana, you may use Urza to make infinite copies of any artifacts you control.