Scrum: My manager always adds sprint items in between

Hi all, We as a team are frustrated and hence want to know what other people on Blind think about the scenario. We are a small software development team of 6 people, we have 2 week sprints, our manager does the following from time to time: 1. Changes sprint tasks in between. 2. Adds sprint tasks in between. 3. If we finish all your sprint tasks with even a single or half day left in sprint closure, he assigns another task and pushes to get it done. 4. Blames the team for not completing tasks in sprint if we spill over the sprint. 5. Keeps changing the priority of sprint tasks till last day of sprint. 6. Pushes us hard to have as low story points as possible to fit in maximum tasks. 7. If you are free for even a couple of hours or reading something, assigns a task again. 8. Does not push back for all the bad work which comes to our team. 9. Cannot say no to his management or his peers, accepts what anyone has to say and then pushes down the pressure with stringent timelines. Needless to say, the team feels very demotivated and frustrated under him and we are clueless what to do. Any ideas, how should we tackle him?