Thranduil, the Elvenking, Umbral Mantle, and Woodland Weavemaster

Prerequisites

• Thranduil, the Elvenking on the battlefield
• Umbral Mantle on the battlefield
• Woodland Weavemaster in the graveyard

Steps

1. Activate Thranduil using Woodland Weavemaster's ability by tapping it, adding an amount of mana equal to Thranduil's power that can only be spent to cast Elf spells or activate abilities of Elves
2. Activate Thranduil using the ability granted to it by Umbral Mantle by paying and untapping it, giving it +2/+2 until end of turn
3. Repeat

Results

• Infinite colored mana that can only be spent to activate abilities of certain creatures
• Infinite colored mana that can only be spent to cast spells of a certain creature type
• Infinitely large creature until end of turn