There we go. I wonder how relevant the drawback is.

How relevant it is is highly dependent on the environment it's found in.

As he is now, this guy here is definitely better than its closest comparison, Watchwolf (albeit in different colors). Now, being better than Watchwolf isn't inherently a bad thing -- after all, Fleecemane Lion was strictly better than Watchwolf, too. The first problem here is that Watchwolf and Fleecemane were white/green -- that is to say, both of the colors that get efficient creatures. This guy isn't. And while a downside helps a lot with that, unless it's in a very tap-heavy environment (Which doesn't happen very often) then I don't think that the downside is enough here. I would say it's fairly close to being balanced though, and since I'm hardly an expert that probably means it's fine the way it is. You could drop its power or toughness by one or make it a 3/4 for 1BW if you really wanted to be safe I suppose.

...My reply was a lot less meandering when I started typing it, I swear.

Woah, thanks for such a complete reply! I should probably drop this guy's toughness by one, as one can tell from the rules text, he was never intended to be very survivable :)