The entire combat system is just a highly complex, beautifully animated game of Rock, Paper, Scissors.

This guide will break down the combat triangle and show you how to exploit it to guarantee positive elixir trades.
The Core Mechanics
For example, a massively expensive P.E.K.K.A (Single-Target) will absolutely destroy a Wizard (Splash) in a one-on-one fight.

Finally, the Wizard (Splash) will incinerate the entire Skeleton Army (Swarm) in a single fiery blast, completing the circle.
Only launch a Swarm attack when you know their Splash unit is not in their hand.Always consider the Z-axis.Sometimes, playing into a counter is necessary to fix your hand. Breaking the Triangle
Once you understand the basic Rock-Paper-Scissors rules, you can begin to actively subvert them using 'Bait' strategies.

You are no longer playing the cards on the screen; you are playing the player behind the screen.
Unit CategoryWhat it BeatsThe CounterThe HordeHigh DPS single-target tanks, Princes, P.E.K.K. For more info about tower rush take a look at the website. AsWizards, Valkyries, Bomb Towers, The LogAoE UnitsSkeleton Armies, Minion Hordes, Goblin GangsHigh health single-target units, Mini P.E.K.K.As, Heavy Spells The Evolution of Balance
If Splash units become too strong, nobody will play Swarms, and Single-Target units will dominate the ladder.

Master the triangle, and the trophies will follow naturally.