In Chapter 27, what three incidents concerning Ewell occur? From these incidents and from Atticus, what do we learn about Bob Ewell?

Bob Ewell found acquired and lost a job, which led to him finding that his notoriety had been fleeting and he was no longer a local "celebrity".  Someone entered Judge Taylor's home without permission, which scared him.  Link Deas became aware of the Ewell family's (specifically, Bob's) harrassment of Helen Robinson and put an end to it by making Bob aware that it was not a secret and that Deas would charge him with assault if it continued.

The three incidents concerning Bob Ewell in Chapter 27 make it evident that Ewell is still consumed with matters of (false) pride, as he had been during the trial, and that he is a coward.  While Ewell is cowardly, he is also vindictive; this sort of person can be extremely dangerous.  It is evident that Ewell does intend to exact revenge on those he feels wronged him (primarily through embarrassment) and that he will do it through sneaky ways, rather than being "up front" and honest.