Dreamstalker Manticore

Whenever you cast your first spell during each opponent's turn, Dreamstalker Manticore deals 1 damage to any target.

Omen of the Sea

Flash
When Omen of the Sea enters the battlefield, scry 2, then draw a card.
{2}{U}, Sacrifice Omen of the Sea: Scry 2.

Whenever you cast your first spell during each opponent's turn, you may tap or untap target nonland permanent.

Whenever you cast your first spell during each opponent's turn, draw a card.

Counter target creature or enchantment spell. If that spell is countered this way, exile it instead of putting it into its owner's graveyard.

Draw a card.
Escape—{2}{U}, Exile five other cards from your graveyard. (You may cast this card from your graveyard for its escape cost.)

Flash
When Omen of the Forge enters the battlefield, it deals 2 damage to any target.
{2}{R}, Sacrifice Omen of the Forge: Scry 2.

Whenever you cast your first spell during each opponent's turn, put a +1/+1 counter on Arena Trickster.

Flying
Whenever you cast your first spell during each opponent's turn, Mischievous Chimera deals 1 damage to each opponent. Scry 1.