Urza, Lord High Artificer, Nim Deathmantle, and Ashnod's Altar

Prerequisites

• Urza, Lord High Artificer on the battlefield
• Nim Deathmantle on the battlefield
• Ashnod's Altar on the battlefield

Steps

1. Activate Urza's second ability twice by tapping Nim Deathmantle and Ashnod's Altar, adding
2. Activate Ashnod's Altar by sacrificing Urza, adding
3. Nim Deathmantle triggers, causing you to pay to return Urza from your graveyard to the battlefield and attach Nim Deathmantle to it
4. Urza enters the battlefield, creating a 0/0 Construct artifact creature token with "This creature gets +1/+1 for each artifact you control"
5. Activate Urza's second ability by tapping the Construct, adding
6. Activate Ashnod's Altar by sacrificing the Construct, adding
7. Repeat from step 2
8. Once you have infinite mana, you may repeat the loop while skipping step 6, resulting in infinite Construct tokens, and you may activate Urza's last ability any number of times

Results

• Infinite blue mana
• Infinite colorless mana
• Infinite creature tokens
• Infinite death triggers
• Infinite ETB
• Infinite LTB
• Infinitely large Construct tokens
• Infinite sacrifice triggers
• Play all cards in your library without paying their mana costs
• Exile your library
• Cast all cards in your library without paying their mana costs