#2 Injure Seth Rollins
Dean Ambrose spent a long time on the sidelines after his injury put him out of commission for around nine months. During that time, he sat back and watched as his Shield-mates somehow got on fine without him.
In fact, they did quite well for themselves. Roman Reigns was finally able to overcome the obstacle of 'The Beast Incarnate' and win the WWE Universal Championship.
On the other side of things, Seth Rollins replaced Ambrose with Jason Jordan and actually managed to win the WWE Tag Team Titles again. Later, during his singles run, Rollins put on match after match which set him apart from the rest of the roster, as everyone sat up and took notice.
Meanwhile, what was Dean Ambrose doing?
He was sitting at home training to come back, but unable to do anything while his friends left him behind and continued to perform week after week as if he had never existed.
If there is one thing that Dean Ambrose would like to do to Seth Rollins, it is to return the favour. Being replaced by Jordan within a week could not have felt good. Dean Ambrose could try to injure Seth Rollins and put him on the shelf.
This would be justice in his rage-crazed mindset and would give him the right to have a run for the titles and be the Shield member who is in the spotlight for once.