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FIRE

The Lava King commands all the Fire units and is guarded by Rock Golem sentries.
Erupt your volcano to gain access to more abilities.
Fire units consume wood for fuel making them strong against Nature units.

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SPARKS

Brawler unit. Sets the enemy on fire.

These three work together to deliver a powerful moderate burn.
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SMOKE

Tank unit. Attacks seem to go right through it.

Has a hard time breathing.
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SPITTING FLAME

Ranged unit. Upgraded attacks shoot farther.

Lights up areas so they are easier to see, unless it just likes burning things.
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COAL

Support unit. Grants smolder to allies. Smolder lets allies live a little longer after they are defeated.

Very giving for having a heart of coal.
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BOULDER

Spellcaster unit. Stuns enemies.

No one is more bold.
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LIGHTNING

Assassin unit. Initial impact deals bonus damage.

If you see one up close it will be very bright! followed by a lifetime of darkness.
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LAVA MONSTER

Massive unit. Grows stronger with nearby allies.

Eats so fast it gets heartburn.