Cards in the Core Set are compatible with cards from other sets, though certain cards from one set may not be as effective in another one.
When the same characters or cohorts appear in different sets, they are represented with different cards having different abilities and powers. To distinguish between them, we add the name of the set the card came from to the card name. For example, "Core Set Ezren" is a different card than "Rise of the Runelords Ezren," so you may not exchange roles between them.
Older cards sometime used slightly different rules and terminology; see the Transition Guide section for more details.