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.
Resolve the Brinelin trigger, returning 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.