Players should note that troops can be upgraded in the Laboratory. Tier 1, Tier 2 and Dark Elixir Troops receive a major graphic change at level 3, and another at both levels 5 and 6, if applicable. Tier 3 troops receive graphic changes with all upgrades. As troops are upgraded they become more powerful, but also cost more Elixir (or Dark Elixir) to train.
Tier 3 troops (Healers, Dragons and P.E.K.K.As) are extremely powerful and are a valuable part of a very powerful army, being able to to overwhelm defenses easily. However, they are extremely expensive in terms of Elixir cost.
Dark Elixir Troops (Minions, Hog Riders, Valkyries, Golems, Witches and Lava Hounds) are troops that fill specific niches that the regular troops do not, like inexpensive flying troops, wall avoidance, powerful ground-based splash damage and massive health. They are not necessarily more powerful than their Elixir-based counterparts, but can be used in very effective ways if deployed properly.
Heroes (Barbarian King and Archer Queen) are immortal troops that are summoned via a permanent altar rather than trained in a Barracks. They are the most powerful troops in the game, but each player may only have one of each type. Although they cannot die in battle, they can be defeated and must rest for a period of time if they take damage.
Spells are created in the Spell Factory. Upgrade your Spell Factory to get more spells and to be able to hold more spells. You can also research spells in the Laboratory to make them more powerful.