Every Fiend is tied to a specific color. For example, Temper is a green fiend. This means that you should match his color until he throws his special block (a green horizontal bomb) into the game grid. You use these special blocks by matching another similarly colored block with them. You always need to match at least 3 blocks of the same color for the move to qualify.
You can tell which color each Fiend is by the colored circle underneath them!
Fiend colors: Purple - Red - Green - Blue - Yellow
Fiends have a variety of special blocks at their disposal that fall into a few common categories.
Bombs are the most common special block type, they deal a lot of damage to slugs, and come in different directional varieties. You can see the direction in which the bomb will blow up by the icon on top of it. When activating a bomb, white circles indicate which blocks it will blow up. Use these "targeting circles" to hit target blocks like crates and diamonds to collect them!
Note that when making matches, the bomb will follow your finger - allowing you greater control over where you want it to explode.
A Horizontal Bomb with its targeting circles
Fiends with the Converter special block (like Kwincy!) are great at collecting more blocks of their color. When a converter is activated it turns all of its surrounding blocks into the same color. Converter fiends are best used in levels where there is a specific color objective - for example, to collect 50 yellows. They don't do as much damage to slugs as Fiends with a bomb special block.
Note: you can never start a match with a converter, but rather you must always get at least one block of a matching color next to it so that you can trigger it!
Activate a converter by dragging a match from a similarly colored block!