By filling your side of the map with passive buildings that constantly generate cheap units, you force the opponent to spend all their elixir simply trying to survive.

This article details the absolute best cards and strategies required to build the ultimate, unbreakable Spawner deck.
The Core Engine: Selecting Your Buildings
The Furnace provides massive splash-damage value, instantly killing enemy swarms and forcing the opponent to respond to the fire spirits before they connect with the tower.

Place your Goblin Hut safely behind your Princess tower, and place your Furnace aggressively in the center to pull enemy tanks into the crossfire.
The Tombstone is an excellent cheap addition.If they just used their Fireball on your tower, you have a safe 10-second window to place your new hut.Your goal in single elixir is simply to set up one or two buildings and survive. The Support Cards
Cards like the Flying Machine or Dart Goblin are perfect because they can sit safely behind your wall of huts and snipe enemy attackers from a distance.

If they drop a Wizard behind their tower to clear your goblins, you instantly Poison the Wizard and the tower simultaneously, gaining massive value.
Spawner CardWhat it DoesPlacement ZoneGoblin Hut (5 Elixir)Constant anti-air chip damage and spell baitSafely behind the Princess tower or deep in the cornerFurnace (4 Elixir)Splash damage pressure and swarm controlAggressively in the center to pull tanks and pressure the bridge Suffocating the Opponent
You are daring the opponent to break through an infinite wall of meat shields.

They will run out of spells long before you run out of troops.

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