Letter Quest: Grimm's Journey Remastered

Crystals appear randomly and have various bonus effects depending on their color. In general they will stay on the board until you use them or an enemy uses an attack to destroy them by turning them into poison, spike, plague, etc., tiles.

Once you have one tile on the board, purposely avoid using it until a second tile shows up, then use both tile letters in the same word and the achievement will unlock.

To increase the chances of crystals showing up, there is an upgrade that can be upgraded to increase the chance for crystals showing up. I wouldn't recommend spending gems on this early though since this achievement will likely come naturally without needing an upgrade for it.