Aside from extra combat steps, I can hardly think of relevant scenarios where this isn't just generally better vigilance. That's rather concerning, especially as you've stretched it out for bant colors, where vigilance is rarely seen in green (secondary there these days though) and isn't officially part of blue outside of planar chaos.

Blue definitely gets to play with untapping though. Having the ability on utility creatures rather than stompies makes sense.

And beating your opponent to death with an unusually large Llanowar Elves is a very traditional green thing to do :)

But yeah, you do want to be a bit careful with the ability. Putting it on a big combat creature would be a bit too much like 'it is vigilance but easier to mess up'

Yes, I mostly intend it for tap/untapping utility stuff, which does jibe with blue. It is technically "better vigilance". Not especially intended for big combat creatures, for the most part. Nothing higher than 3/3. In most cases with the ideas I'm playing with here, its part of a utility function with the rest of the what the card does, rather than as part of a combat function.

Cards with this ability also get progressively stronger the more players there is. (((Scentless Apprentice))) can untap creatures equal to the number of players, which seems fine-ish. With this particular card that could be seen as favorable as well, but it could end up having some issues. For example, (((Yaados Mystic))) enchanted with Oracle's Insight in a 3+ player match would get old really fast.

I am a little ambivalent about (((Yaados Mystic))), as a 2 mana card that can potentially do a lot of damage/give a lot of power out the gate. Perhaps I could warp it to be more balanced as a 3 mana card.

It is a fair point that I'm going to have to be a little careful in trying to impliment this mechanic. At the moment, this is a bit of a big brainstorm on the possibilities opened up by it. I think as long as it's used carefully it can be really flavorful and open up some fun gameplay.