Each event has specific rules. These rules define what is required to score points as well as changes in the normal match or other restrictions.
The only requirement for Events is, for clan based Events. If you are not in a clan you will not see or be able to participate in clan events. All other Events can be played by everyone that is at least Area 2.
Event matches do not affect keys, your star rating, victory bonus or victory points.
In Event matches your current Event Level defines the Level or your Hero and Spells. The match Level is always based on the lowest Event Level of both players.
You are currently Event Level 5 and your enemy is Event Level 6 the lowest Event Level would be 5.
You use a level 4 Hero and Level 3 and 4 Spells these Spells and Hero Level stay the same.
The enemy has a Level 8 Hero and Level 10 and 9 Spells and a level 4 spell, his Spells and Hero will be capped to Level 5, except for his level 4 spell which stays the same.