See The Best Butcher. I like this iteration more, but it's eats up a lot of the text box. Current ideas regarding Maestro are that cards can care about Maestros.

This seems really cool.

Big problem though, neither of these cards work. Right now, Maestro has a parameter, but nowhere does it say you need to pay that cost. So why is it there? Did you mean to include that you have to pay the cost, or does Maestro not have a cost?

I agree it would be nice to cut down on space in the reminder, I'd suggest removing the +1/+1 counter. If cards care about being Maestro's, you don't need to also care about having counters. Also, it means you don't have to print all your creates under-curve if they have cheap Maestro costs, which could get awkward and limit design space.

So, maybe something like, (Whenever this creatures becomes the target of a spell or ability, if it's not a Maestro, you may pay PARAM1. If you do, it becomes a Maestro.)

Still long, but not as long.

Just an FYI, this triggers on any spell or ability that targets it, including your own. I assume that was intentional, though.

Edit: If you didn't mean to include a parameter, then the wording would be, ("Whenever this creatures becomes the target of a spell or ability, if it's not a Maestro, it becomes a Maestro.")

In my haste I forgot to include that there is a parameter in the reminder text. The +1/+1 counter in this case was to help remind players a creature became a Maestro. This was from feedback I received from another mechanic that I had been testing out before. If this were a digital cardgame, then absolutely I would not worry about having to include the +1/+1 counter to remind players though.

"The +1/+1 counter in this case was to help remind players a creature became a Maestro"

That's actually a pretty good reason to include one.