You have at least seven cards in your graveyard and/or exile that's an instant or sorcery, or that has an Adeventure.
Dragons you control have a total mana value of five or greater.
Steps
Activate
Gwenna by tapping it, adding ({U} magic symbol) ({U} magic symbol) that can only be spent to cast creature spells or to activate abilities of creatures.
Earthquake Dragon from the battlefield to your hand.
Resolve the
Gwenna trigger, putting a +1/+1 counter on it and untapping it.
Activate
Gwenna by tapping it, adding ({G} magic symbol) and one mana of any color that can only be spent to cast creature spells or to activate abilities of creatures.
Cast
Earthquake Dragon by paying ({G} magic symbol) .
Brinelin and
Gwenna trigger.
Resolve the
Brinelin trigger, returning
Sailors' Bane from the battlefield to your hand.
Resolve the
Gwenna trigger, putting a +1/+1 counter on it and untapping it.
Repeat.
Results
Infinite +1/+1 counters on
Gwenna.
Infinite colored mana that can only be spent to activate abilities of creatures.
Infinite colored mana that can only be spent to cast creature spells.