I really like the ideas for the Overlord class. Looking at these cards, I have some suggestions/comments:
Power Lock - "Play this card at the start of your turn. For each hero, choose 1 class skill card to make inactive. Inactive skills cannot be used until the start of your next turn."
Does magic seal affect just 1 hero or all heroes (like Power Lock)?
Magic Seal - "Play this card at the start of your turn. Choose 1 hero. That hero's ability is inactive and cannot be used until the start of your next turn."
Magic Seal - "Play this card at the start of your turn. All hero abilities are inactive and cannot be used until the start of your next turn."
Restrained - "Play this card at the start of a hero's turn. Until the start of their next turn, that hero cannot use their heroic feat." Is your intention for this to also affect all heroes or just one?
Warping - "At the end of your turn, place this card in your play area. Select one monster from the map and set it on this card. At the start of your turn, discard this card and place the monster within 3 spaces of a hero. That monster may immediately perform an attack that is not part of its regular activation." I figured you meant a monster that was already on the map, but if not, you could adjust the wording.
Did you want Enfeeblement Aura to be a permanent buff for any OL card? Some cards say "...start of your turn", "...start of hero turn", "...end of your turn", "...end of hero turn", etc.. Also, does this card count towards the 15 card deck size or not?
Enfeeblement Aura - "When purchased, place this card in your play area. This card cannot be discarded or shuffled into your deck. When applicable, effects from Overlord cards last 1 additional turn. This card does not count towards your desk size."