"Elder" or "Dinosaur" chosen with Mirror of the Forebears.
It is your precombat main phase.
({6} magic symbol) ({R} magic symbol) ({R} magic symbol) ({R} magic symbol) plus enough mana to pay for commander tax, if applicable available.
Steps
Cast Etali either from your hand or from the command zone by paying ({5} magic symbol) ({R} magic symbol) ({R} magic symbol) plus commander tax, if applicable.
When Etali enters the battlefield, it triggers.
Holding priority, activate Mirror of the Forebears by paying ({1} magic symbol) , choosing to have it become a copy of Etali until end of turn.
Choose to put Etali into your graveyard due to the legend rule.
If Etali is your commander, choose not to return it to the command zone from your graveyard.
Hua Tuo triggers, untapping itself.
Activate Hua Tuo by tapping it, putting Etali on top of your library from your graveyard.
Resolve the Etali trigger from step 2, causing you to exile cards from each player's library until you exile a nonland card, with you exiling Etali from your library, and cast Etali and any other nonland cards exiled this way without paying their mana costs.
Choose to put Etali into your graveyard due to the legend rule.
If Etali is your commander, choose not to return it to the command zone from your graveyard.
Etali enters-the-battlefield ability and Hua Tuo trigger.
Resolve the Hua Tuo trigger, untapping it.
Repeat from step 7.
Results
Cast all nonland cards from each opponent's library.