When Siege-Gang Commander enters the battlefield, it and Mana Echoes trigger.
Resolve the Siege-Gang Commander trigger, creating three 1/1 Goblin creature tokens.
When the Goblin tokens enter the battlefield, Mana Echoes triggers three times.
Resolve all four Mana Echoes triggers, adding at least ({16} magic symbol) .
Activate Gemstone Array four times by paying ({8} magic symbol) , adding ({W} magic symbol) ({R} magic symbol) ({R} magic symbol) ({R} magic symbol) .
Activate Siege-Gang Commander by paying ({C} magic symbol) ({R} magic symbol) and sacrificing itself.
Sigil of the New Dawn triggers, causing you to pay ({C} magic symbol) ({W} magic symbol) to return Siege-Gang Commander from your graveyard to your hand.
Resolve the Siege-Gang Commander activated ability, dealing 2 damage to any target.