Please note a few things regarding Dancing Scimitar in conjunction with the FM.
1. The Dancing Scimitar has an upkeep of 1. So not only does it cost the FM 5 to cast but to keep it around the FM has to spend an additional 1 each round. That's a plus to you.
2. The scimitar can only be used once per turn either for defending or for attacking for 3 dice. Not both. In 'most cases' FM builds try to overwhelm and kill their opponents as fast as possible. What this means is if they are using their scimitar to defend then that is essentially saving you from 3 dice of damage per turn. The longer you stay alive the better you will do against a FM.
3. Even if they decide to to defend with the scimitar they only do so on a 8+. So the chance of defending your attack is really only 42.67%. So more often than not will your creatures attack go through. Don't forget, regardless of a successful or unsuccessful defence, point 2 above comes into play. (You don't get hit for 3 dice of damage from the scimitar).
4. As mentioned the scimitar is a quick cast for 5 mana plus the upkeep of 1. Lets say on your end you cast a Bitterwood Fox (just as an example) which is also a quick cast (for the BM) for 5 mana and with no upkeep. So right off the bat it is essentially cheaper due to the lack of upkeep. The Bitterwood Fox can do 3 dice of damage. If you attack with the fox the FM has two choices regarding the scimitar.
a) Use the scimitar for a 42.67% chance to defend 3 dice of damage from the fox or
b) Don't use the scimitar to 'potentially' defend 3 dice of damage and then during the FMs action deal 100% guaranteed 3 dice with the scimitar to the BM. (Basic use case scenario, not taking into account possible damage mitigation like armor).
If I were the FM I would choose the latter. If they choose to defend that's a solid plus for you I'd say.
5. "But then the FM just turns around and kills my fox." A FM does a lot of damage. Galvitar, Hands of Bim Shalla, Strength Gloves, Battle Fury and so on. If they waste an entire turn attacking a fox dealing untold dice to the fox and killing it that means you were just saved all of that damage. Again this means you live longer and have a higher chance of defeating the FM.
6. "What if I'm not attacking with a fox but with a creature that has more dice to roll". Well regardless of how many dice you are attacking with the chance of them defending with the scimitar is still only 42.67%, so they need to decide is having a 42.67% chance of blocking even say 5 dice worth it? When compared to having 100% to dealing 3 dice of damage.
Essentially what I'm getting at is that if the FM is using the scimitar to block then in the majority of cases I would argue that's most likely a benefit to you as a BM.
Thanks!
Alpha