We should know at least an average chance to hit. If we are fighting a new type of opponent, we may not know enough to be given the actual chance to hit.
You can use items during combat (loot, drop gold as a distraction for some types of opponents, etc). I don't know about giving another character items in combat, but normally you can just drag and drop an item onto a character's portrait to place something in their inventory.
There are other forms of magic, like curses or warrior/survivor skills.
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