When I use a spell such as Revenge on my Barbarian sometimes I will get a critical strike number that is rather high. Is this number that displays the number of my critical strike on one enemy, all enemies combined, or each enemy.
Revenge does NOT do one damage applied to multiple monsters, instead each monster is separately and their damage is applied to individually. So to anwser your question that critical strike would only be applied to the one monster.
If I have a critical chance of lets say 20% and I am fighting 10 monsters. I will probably get a critical hit for two of the monsters. They will individually get whatever the critical hit damage was to them. So if I do 100 damage hit with critical damage dealing 200 damage (made up numbers). Now for argument sake lets say Monster 3 and Monster 9 have high defense and reduce damage by 10%.
The damage for the monsters would be
Monster 1: 100 | Monster 2: 100 | Monster 3: 180 | Monster 4: 100 | Monster 5: 100 | Monster 6: 200 | Monster 7: 100 | Monster 8: 100 | Monster 9: 90 | Monster 10: 100 |
What this means is that each monster would take 100 damage except for the ones it crited on they would take 200 damage. The game treats them as invidual htis so the monsters with high defense get hit less.