Thanks a lot for the feedback^^! I'm having a lot of fun writing this fanfic and I'm glad you are enjoying it.
I understand why you think some of the things are a little bit weird so maybe I can shed some light on it for you.
1. I'm pretty sure the characters are a year older than from the first movie. I do realize that it would still be unlikely for them to take on sharpteeth, but like you said I wanted to add some more mature elements into LBT while keeping it true to the original material. One of the things I had visioned was that the gang was sick and tired of always running away from sharpteeth. This time when they see sharpteeth, mostly fast biters, they feel some uncontrollable adrenaline which causes them to feel able to fight them. Of course, if they were to encounter a larger sharptooth like Red Claw they would still run away, like they did in the first Revenge, but since the fast biters are closer to their size they feel more able to fight them. Hopefully that makes some sense, but if you're still a little odd I can understand.
2. With Blacktail, I wanted to make him more than just another standard villain. With Rinkus and Sierra, they are more credible as villains because you know virtually nothing about them but you hate what they do or attempt to do to Littlefoot and his friends. On the other hand, you know why Blacktail hates Littlefoot and his friends, so he's a much deeper and more developed villain. It causes the reader to be torn with whether or not to sympathize him or disregard his history with his father and hate him based on what he is doing in the present. Also, Blacktail still has some evil left in him that he hasn't shown yet, so when the next chapter comes around hopefully you will see what I mean.
Anyway, I hope this explains my reasoning behind why everything is the way it is in my story. You have any other questions you can ask me.