Hiya - thanks heaps for the help!!
I noted there was already a DamageType_Enum with Basic / Poison / Stun (not implemented)… this is used in the Card_Struct.
I went ahead and created a new AbilityDamageType_Enum and added it to the Ability Struct, created the AbilityDamageType variable in 3dcard blueprint and followed instructions above. Worked exactly as intended from testing. I now have cards that can atack multiple times / multiple targets with and without retaliation… and the retaliation loop error is gone.
Sweet as 
Now time to try and impliment the base DamageType Poison and Stun on initial attack…