Seething Pathblazer

Sacrifice an Elemental: This creature gets +2/+0 and gains first strike until end of turn.

Lightning Elemental

Haste (This creature can attack and {T} as soon as it comes under your control.)

Air Servant

Flying
{2}{U}: Tap target creature with flying.

Smokebraider

{T}: Add two mana in any combination of colors. Spend this mana only to cast Elemental spells or activate abilities of Elementals.

Bramble Creeper

Whenever this creature attacks, it gets +5/+0 until end of turn.

Swamp

Regathan Firecat

Bloodpyre Elemental

Sacrifice this creature: It deals 4 damage to target creature. Activate only as a sorcery.

Inferno Elemental

Whenever this creature blocks or becomes blocked by a creature, this creature deals 3 damage to that creature.

Primal Plasma

As this creature enters, it becomes your choice of a 3/3 creature, a 2/2 creature with flying, or a 1/6 creature with defender.

Forest

Brighthearth Banneret

Elemental spells and Warrior spells you cast cost {1} less to cast.
Reinforce 1—{1}{R} ({1}{R}, Discard this card: Put a +1/+1 counter on target creature.)

Whisperwood Elemental

At the beginning of your end step, manifest the top card of your library. (Put it onto the battlefield face down as a 2/2 creature. Turn it face up any time for its mana cost if it's a creature card.)
Sacrifice this creature: Until end of turn, face-up nontoken creatures you control gain "When this creature dies, manifest the top card of your library."

Mournwhelk

When this creature enters, target player discards two cards.
Evoke {3}{B} (You may cast this spell for its evoke cost. If you do, it's sacrificed when it enters.)

Cytospawn Shambler

Graft 6 (This creature enters with six +1/+1 counters on it. Whenever another creature enters, you may move a +1/+1 counter from this creature onto it.)
{G}: Target creature with a +1/+1 counter on it gains trample until end of turn.