How about a 2500 pound baby chick?
Tigers are fluffy, but they're still plenty scary.
Also, large "fluffy" birds are pretty imposing. Ever been up close and personal with an Ostrich? I had a bunch surround my car in a nature preserve, it felt like a scene out of "Jurassic Park".
As for the fluffy T-Rex, picture being a mouse next to a nice, fluffy eagle which is looking you over. Or as in "A Bug's Life", being a grasshopper next to a songbird. Being big enough to rip you apart without breaking a sweat has a way of being scary, no matter how fluffy.