Saheeli, the Sun's Brilliance, Mana Echoes, Great Oak Guardian, and Signpost Scarecrow

Prerequisites

• Saheeli, the Sun's Brilliance on the battlefield
• Mana Echoes on the battlefield
• Great Oak Guardian on the battlefield
• Signpost Scarecrow on the battlefield
• Saheeli does not have summoning sickness
• available, plus an additional if you control less than three creatures that share a creature type with Great Oak Guardian

Steps

1. Activate Saheeli by paying and tapping it, creating a token copy of Great Oak Guardian with haste
2. When the token Great Oak Guardian enters the battlefield, it and Mana Echoes trigger
3. Resolve the Great Oak Guardian trigger, untapping all creatures you control and giving them +2/+2 until end of turn
4. Holding priority, if you control less than four creatures that share a creature type with Great Oak Guardian, repeat steps 1 through 3 one additional time
5. Resolve all Mana Echoes triggers, adding for each creature you control that shares a creature type with Great Oak Guardian for each trigger resolved this way
6. Activate Signpost Scarecrow twice by paying , adding
7. Repeat

Results

• Infinite ETB
• Infinite colored mana
• Infinite colorless mana
• Infinite creature tokens with haste
• Infinite untap of creatures you control
• Infinitely large creatures you control until end of turn