Magic The Gathering - Jace, Cunning Castaway's +1
You draw cards equal to the number of combat damage steps where your creatures have dealt damage.

If you attack with any number creatures, none having first strike or double strike, there is only one combat damage step. The delayed trigger will be met once.

If the creatures you control do damage during the first strike and the non-first strike combat damage step (eg. a creature with double strike or mix of creatures with and without first strike), the delayed trigger will be met twice.

If you have multiple combat phases during the same turn, the delayed trigger will be met once for each non-first strike and first strike combat damage step that occurs. 

Combat damage is dealt all at once (or in two steps if you have first/double strikers) instead of once per creature. To break it down (simplified) combat looks like this:


Attacking Player declares attackers
Defending Player declares blockers
Combat Damage Step (Comp Rules 510):
a. If at least one creature has First Strike or Double Strike, only creatures with first strike or double strike assign damage this step.
b. Players announce how their creatures will assign damage (eg. Attacker is blocked by multiple creatures, trample etc.)
c. All assigned damage is dealt simultaneously. (Jace's Ability Triggers here).
d. If this Damage step was for first/double strikers only return to step 3.b but this time all creatures except first strikers get to assign damage. If not proceed to step 4.
End of Combat Step