Fanatic of Xenagos

Trample
Tribute 1 (As this creature enters the battlefield, an opponent of your choice may put a +1/+1 counter on it.)
When Fanatic of Xenagos enters the battlefield, if tribute wasn't paid, it gets +1/+1 and gains haste until end of turn.

Pharagax Giant

Tribute 2 (As this creature enters the battlefield, an opponent of your choice may put two +1/+1 counters on it.)
When Pharagax Giant enters the battlefield, if tribute wasn't paid, Pharagax Giant deals 5 damage to each opponent.

Flame-Wreathed Phoenix

Flying
Tribute 2 (As this creature enters the battlefield, an opponent of your choice may put two +1/+1 counters on it.)
When Flame-Wreathed Phoenix enters the battlefield, if tribute wasn't paid, it gains haste and "When this creature dies, return it to its owner's hand."

Snake of the Golden Grove

Tribute 3 (As this creature enters the battlefield, an opponent of your choice may put three +1/+1 counters on it.)
When Snake of the Golden Grove enters the battlefield, if tribute wasn't paid, you gain 4 life.

Shrike Harpy

Flying
Tribute 2 (As this creature enters the battlefield, an opponent of your choice may put two +1/+1 counters on it.)
When Shrike Harpy enters the battlefield, if tribute wasn't paid, target opponent sacrifices a creature.

Nessian Wilds Ravager

Tribute 6 (As this creature enters the battlefield, an opponent of your choice may put six +1/+1 counters on it.)
When Nessian Wilds Ravager enters the battlefield, if tribute wasn't paid, you may have Nessian Wilds Ravager fight another target creature. (Each deals damage equal to its power to the other.)

Siren of the Fanged Coast

Flying
Tribute 3 (As this creature enters the battlefield, an opponent of your choice may put three +1/+1 counters on it.)
When Siren of the Fanged Coast enters the battlefield, if tribute wasn't paid, gain control of target creature.

Nessian Demolok

Tribute 3 (As this creature enters the battlefield, an opponent of your choice may put three +1/+1 counters on it.)
When Nessian Demolok enters the battlefield, if tribute wasn't paid, destroy target noncreature permanent.

Ornitharch

Flying
Tribute 2 (As this creature enters the battlefield, an opponent of your choice may put two +1/+1 counters on it.)
When Ornitharch enters the battlefield, if tribute wasn't paid, create two 1/1 white Bird creature tokens with flying.

Oracle of Bones

Haste
Tribute 2 (As this creature enters the battlefield, an opponent of your choice may put two +1/+1 counters on it.)
When Oracle of Bones enters the battlefield, if tribute wasn't paid, you may cast an instant or sorcery spell from your hand without paying its mana cost.

Thunder Brute

Trample
Tribute 3 (As this creature enters the battlefield, an opponent of your choice may put three +1/+1 counters on it.)
When Thunder Brute enters the battlefield, if tribute wasn't paid, it gains haste until end of turn.