Description from the Publisher:

Selecting the troops that you'll lead into battle is only the first step in creating your own Star Wars: Legion army. Once you've supplemented your armies with fresh recruits, you can further enhance them with the addition of upgrade cards. Each upgrade unlocks new tactical possibilities for your army, giving you the freedom to customize your units to meet your individual preferences. While every Unit Expansion contains a variety of upgrade cards that help enhance that particular unit's natural abilities, the Upgrade Card Pack conveniently puts a vast library of upgrade cards at your fingertips no matter which faction you play.