What makes Adopt Me successful is not the specific visual style of our pet designs. I urge you to come up with something original, interesting and unique that fits the style and purpose of your game 
- rather than risk being labeled a copy, and a poor one at that
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Think my favorite case of "Being a copy isn't going to help in the long run" was a copy of Pet Simulator which was basically the same except it used R15 Robloxian rigs instead of boxy pets. Forget being a copy, they've already taken a big blow in performance from that difference.
The original quoted tweet says it all - adopt me isn't popular because of the specific 3D style of our pets lol. but it's easier to rip off a visual style (that Bethink and our other artists spent a long time cultivating) than to innovate
