consider adding an additional U to the cost to make this less splashable and less powerful. Or make it uncommon

This will almost universally be less powerful than Keep Watch (a card that never seemed to fill its destiny as 'bonkers'.) I assume that means this card could cost without ruffling too many feathers.

Normal I would agree but attacking is a far stricter requirement than tapping in this environment due to Emulate and the large amount of activated abilities. that can then be copied to all your other creatures. Maybe keep the current cost and change to uncommon. Often this is going to be equal to either a Concentrate or a Opportunity which is insane for a common.

It's true, this card plays very differently between limited and constructed. The main reason why Keep Watch was never that great a card in constructed, for example, was because any player who controlled three attacking creatures probably already won the game.

But an ability with the potential to explode in block due to inter-block synergies? Yeah, sounds like an uncommon.

That said, I question the wisdom of arguing "Oh, it's not normally a great ability, but it will be awesome in this set. That's why it needs to cost more than it normally would." I would think that that would be the exact reason why you'd want to cost the card as efficiently as possible - as a way to stress the positives of the block, as opposed to protecting the rest of Magic from a linear mechanic.

That would be like overcharging for all the flickering effects in Avacyn Restored because the set is really strong with flicker. The end result would have been annoying, and full of mixed messages about what sort of deck players are expected to play.

I was saying it should be one or the other, not both. Either increase the price so it can be a common without warping the format OR make it a good build around uncommon at its current cost.