Anti atarka card

At first one might assume this effect belongs into white, because it is rule setting. But blue is the enemy color to both red and green, the primary fight colors.

The ability could use better wording. Either of:

• Creatures can't fight.
• Spells and abilities your opponents control can't cause creatures to fight.

On a wider scope there is the issue with one-sided fighting, which does mechanically do something similar to fight, but doesn't outright use the term fight and hence doesn't get recognized by this ability, but as long as you don't put that into this Duel Deck, this card should be fine.

Good choice to make it a creature. Could cost a little less IMO.

Now this seems like it shouldn't be blue, nut white.