It's the biggest wither ever! sadly, it doesn't move or attack, kill it by doing /kill @e[type=WitherBoss] to kill it. why is it named dinnerbone? well... for some reason it turns upside down without the DinnerBone name that normally flips a mob upside down, but this one is reverse... Pretty weird. the way this works is that when you normally summon a wither it becomes bigger in its "Invul" form. that makes it look Blue. once it gets big enough, (default invul on wither is usually invul:5 or so) it turns into its
normal form after. but.. with commands putting this invul number so high makes the game think it is in its growing stage. but it is over the games limit of the code.
Thanks for checking out if you did! credit to NiceMarkMc for showing me this command!