Intensify

Intensify is a new keyword introduced with the Trials of Mythron expansion that will appear on Minions and Spells granting them a powerful stacking effect. These cards become more powerful each time you cast them for the duration of the game. This stacking effect only occurs for the digits printed on the card's descriptions, not numbers that are written out.

The formula looks like this: x * n (x = digits printed on card; n = numbers of times the card was played)

Examples: The third Riftwalker will deal 3 damage, the second Accumulonimbus will summon 4 Wind Dervishes.

More information can be found here.