Gwenna triggers, putting a +1/+1 counter on it and untapping it.
Tempting Wurm enters the battlefield, triggering itself and
Cloudstone Curio.
Resolve the
Tempting Wurm trigger, allowing each opponent to put any number of artifact, enchantment, creature and/or land cards from their hand onto the battlefield.
Resolve the
Cloudstone Curio trigger, returning
Grim Wanderer from the battlefield to your hand.
Activate
Gwenna by tapping it, adding ({1} magic symbol) ({B} magic symbol) that can only be spent to cast creature spells or activate abilities of creatures.