Terra, Magical Adept // Esper Terra | Yenna, Redtooth Regent

Cards

Terra and
Yenna on the battlefield (
Terra as
Esper Terra and
Yenna without summoning sickness).

Activate
Yenna by paying ({2} magic symbol) and tapping it, creating a nonlegendary token copy of
Esper Terra.
When the
Esper Terra token enters the battlefield, its first chapter ability triggers, creating a token copy of itself with haste and four lore counters on it.
When the new
Esper Terra token enters the battlefield, its first, second, third and fourth chapter abilities trigger.
Resolve the first and second trigger, creating token copies of any nonlegendary enchantment you control.
Resolve the fourth trigger, causing you to add ({W} magic symbol) ({W} magic symbol) ({U} magic symbol) ({U} magic symbol) ({B} magic symbol) ({B} magic symbol) ({R} magic symbol) ({R} magic symbol) ({G} magic symbol) ({G} magic symbol) and exile the
Esper Terra token.
Resolve the third trigger, creating a token copy of the
Esper Terra token created in step 1 with haste and four lore counters on it.
Repeat from step 3.

If you do not control other nonlegendary enchantments, this combo creates a mandatory infinite loop that'll end the game in a draw unless one of the combo pieces are removed from the battlefield.

This combo has been estimated to be Ruthless (Bracket 4+).