Bladewing the Risen in hand or in the command zone.
"Dragon" or "Zombie" chosen with Molten Echoes.
({3} magic symbol) ({B} magic symbol) ({B} magic symbol) ({R} magic symbol) ({R} magic symbol) plus enough mana to pay for commander tax, if applicable available.
Steps
Cast Bladewing the Risen by paying ({3} magic symbol) ({B} magic symbol) ({B} magic symbol) ({R} magic symbol) ({R} magic symbol) and commander tax, if applicable.
Bladewing the Risen enters the battlefield, triggering itself and Molten Echoes.
Resolve the Bladewing the Risen trigger, choosing not to return anything to the battlefield.
Resolve the Molten Echoes trigger, creating a token copy of Bladewing the Risen.
Put the original Bladewing the Risen into the graveyard due to the legend rule.
When the token Bladewing the Risen enters the battlefield, it triggers, returning the nontoken Bladewing the Risen from your graveyard to the battlefield.
Put the original Bladewing the Risen into the graveyard due to the legend rule.
When the nontoken Bladewing the Risen enters the battlefield, it triggers, returning the nontoken Bladewing the Risen from your graveyard to the battlefield.
Repeat from step 7.
Results
Infinite death triggers.
Infinite ETB.
Infinite LTB.
Return all Dragons from your graveyard to the battlefield.