Zaxara, the Exemplary, Umbral Mantle, and Biomancer's Familiar

Prerequisites

• Zaxara, the Exemplary on the battlefield
• Umbral Mantle on the battlefield
• Biomancer's Familiar on the battlefield
• Umbral Mantle attached to Zaxara
• Zaxara does not have summoning sickness

Steps

1. Activate Zaxara by tapping it, adding two mana of any color
2. Activate Zaxara by paying and untapping it, giving itself +2/+2 until end of turn
3. Repeat

Results

• Infinite colored mana
• Infinitely large Zaxara until end of turn