See Niche Filler.

Green clone concept

­Dual Nature has me partial to the idea that green cloning would want more token clones rather than creature that ETB as a clone. I don't have some detailed flavor for this like Niche Filler, just that a creature calls a packmate for hunting. I guess that sounds white, but I was picturing a generic beast in my head when I thought of the card. I think just copying one's biggest creature would feels very green.

­Pack Hunt was you know so it was originally in that color at least.

As for the mana cost, this is a really bad clone - or perhaps more appropriately Spitting Image, which MaRo seemingly defends surprisingly by stating that " is secondary in cloning." See here.

I also don't see the restriction being that relevant much of the time as I would assume that you tend to want to copy the largest creature by default.

How does this cost more than Clone? Clone already can do this, but also can copy a smaller more useful creature for its abilities or an opponent's creatures. Adding a restriction should reduce the cost rather than increase it.

Being green is not a reason. If you shift an effect into a color, then not at a cost that not even that color wants to play it.

Core 19 even has an even cheaper variant of Clone for your own creatures at uncommon.

Maybe you want this at four mana because a token producing sorcery is easier to recur than a copying creature card, but anything more is plain to much - and the related cards you create seem to follow the example set here.