Appa, Aang's Companion

Flying (This creature can't be blocked except by creatures with flying or reach.)
Whenever Appa attacks, another target attacking creature without flying gains flying until end of turn.

Katara, Heroic Healer

Lifelink (Damage dealt by this creature also causes you to gain that much life.)
When Katara enters, put a +1/+1 counter on each other creature you control.

Kyoshi Warrior Guard

Momo, Rambunctious Rascal

Flying (This creature can't be blocked except by creatures with flying or reach.)
When Momo enters, he deals 4 damage to target tapped creature an opponent controls.

Sledding Otter-Penguin

{3}: Put a +1/+1 counter on this creature.

Sokka, Wolf Cove's Protector

Vigilance (Attacking doesn't cause this creature to tap.)

Black Sun's Zenith

Put X -1/-1 counters on each creature. Shuffle Black Sun's Zenith into its owner's library.

Tundra Wall

Wolf Cove Villager

Deny Entry

Counter target creature spell. Draw a card, then discard a card.

Flying Dolphin-Fish

Flying (This creature can't be blocked except by creatures with flying or reach.)

Spirit

Lost in the Spirit World

Return up to one target creature to its owner's hand. Create a 1/1 colorless Spirit creature token with "This token can't block or be blocked by non-Spirit creatures."

The Terror of Serpent's Pass

Hexproof (This creature can't be the target of spells or abilities your opponents control.)

Turtle-Seals

Water Whip

As an additional cost to cast this spell, waterbend {5}. (While paying a waterbend cost, you can tap your artifacts and creatures to help. Each one pays for {1}.)
Return up to two target creatures to their owners' hands. Draw two cards.

Elephant-Rat

Menace (This creature can't be blocked except by two or more creatures.)

Avatar: The Last Airbender Eternal