Witch's familiar, Common 1g1r
Demonic. Mage.
Attack 2
If last played card was Quick or Swift
attack: N
N = damage dealt by previous card
(Max 8)
Unless things have changed, N cannot be calculated as such. You might be able to have N look up the last card's "Attack" value, but if the attack was a calculation (Sorceress) or nested in an if statement (Dark pegasus) or just wall damage that could have been used against an opponent with little or no wall before the attack (Whirlwind), then it becomes too complicated for the system to determine. You could alternately see how much damage the opponent has suffered this turn rather than by the last card, though then you can have someone chain two Poison frogs for 4 damage or, with future card additions, have a Quick/Swift which increases and decreases wall/tower simultaneously and confuses the calculation.
I would suggest having this card instead deal extra damage based on the rarity of the preceding Quick/Swift, perhaps C:2,U:5,R:8.