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
A true Spawner deck typically utilizes two or three distinct spawning buildings, each serving a different tactical purpose in the overall engine.

The Barbarian Hut is the heavy investment (often costing 7 elixir) and is usually played only in double elixir; it acts as an immovable defensive wall while generating massive, high-health pressure.
It is too expensive and leaves you instantly vulnerable to a fast opposite-lane rush.If the opponent sends a Miner to destroy your Furnace, you must kill that Miner instantly.Delay the placement. Defensive Synergy and Spell Baiting
Because your buildings cost so much elixir, you must fill the rest of your deck with incredibly efficient, cheap defensive support units.

You also need a heavy spell of your own (usually Poison or Fireball) to destroy the opponent's defensive units that get stuck trying to clear your massive swarms.
The SynergyWhy It FitsFlying MachineSits safely behind the river, immune to ground units, forcing the opponent to use spells on it instead of the hutsMother WitchTurns enemy defensive swarms into your own offensive hogs, creating pure, unmanageable chaos on the board The War of Attrition
You are daring the opponent to break through an infinite wall of meat shields.

The siege never ends.

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