Mammoth Rider needs to have consistent position with the mammoth, a proper decay bone leg placement, and a Troll death sound. He also has the same rider model and portrait of the Ice Troll Trapper, is this supposed to be a mounted version of it? Both of the two models also need a more linear transition in Decay animation. But nothing too bad and it's still useable somewhat so I'm putting this to SIMPLE/USEFUL
For HIGH QUALITY: fix the issues, and give an Attack Two animation for Mammoth Rider where the mammoth nudges a bit forward while the rider throws his axes (see Kodo Beast for example), and then an extra Attack 2 where the mammoth charges forward