How do I know how strong the enemy is?

[eXeel]

If you right click the mob group, you can see "health", I believe it is called. That is the damage each mob in the group can take before it dies.

I don't understand your question. Don't you see Attack, Defense, Health, Damage etc, when you right click a mob?
And when you hover over a mob, ready to attack it, doesn't it show how many will die (5-7 for 800-877 damage)?