Molten Echoes and Altar of Dementia on the battlefield.
"Human" or "Soldier" chosen with Molten Echoes.
({2} magic symbol) ({R} magic symbol) ({W} magic symbol) plus enough mana to pay for commander tax, if applicable available.
Steps
Cast Gerrard either from your graveyard or from the command zone by paying ({2} magic symbol) ({R} magic symbol) ({W} magic symbol) and commander tax, if applicable.
Gerrard enters the battlefield, triggering Molten Echoes, creating a token copy of Gerrard with haste.
Put the nontoken Gerrard into your graveyard due to the legend rule.
The nontoken Gerrard dies, triggering its ability.
Holding priority, activate Altar of Dementia by sacrificing the token Gerrard.
The token Gerrard dies, exiling itself and returning the nontoken Gerrard from your graveyard to the battlefield.
Repeat from step 2 an arbitrarily large number of times.
Resolve all Altar of Dementia abilities, causing any number of players to mill infinite cards.