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I'm not sure what you mean. Would you consider DotA to not be 'distinct' or 'separate' from (regular/vanilla/classic) Warcraft 3? It is a 'modification', and in my mind, while it subsists almost entirely of in-game assets, it manages to combine them in a way unique to & from the game itself. It is it's own, new entity.
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The gameplay has been remade. By remade of course, I mean that they've structured the means of acquiring a hero easy, while also making it the only unit you have. This concept is not new. Hero Arena was around before dota was even thought of. If we continue the previous analogy. A mod, is when you skip the paintjob and starts picking out the insides of the car instead. You keep a few of the bare essentials and plug in some new power in there. Allowing the car to access new things that it wasn't built for. If you really wanna change things up. You could give it a paintjob as well.
Although the gameplay mechanics of the heroes remain the same, the gameplay of the map is different. Thus, it's a overhauled concept. Not exactly unique, considering the other offshoots that eventually spawned this, but it's a very creative concept and adds variation to playing blizzard maps.
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Generally, while I agree it can't be said that Ujimasa "made" the Goblin Merchant model, he did model-edit the thing that Planking Wolf wants modified; thus, as the "creator" of that "resource", he should be getting permission. At least in my mind.
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I disagree. The one who made the most work on that model was blizzard and they've already given us the permission to use their stuff in their games.
Here's to continuing the discussion elsewhere.