Scrum Burndown Patterns

Question

I'm in a 10 person team working on a large legacy code base with a less than ideal product owner. Our backlog is in pretty bad shape and large epics have frequently been breaking our sprints. The team also struggles with its definition of done - some members write unit test religiously, others don't, sometimes depending on time available.

So, I've been seeing some interesting burndown patterns, and I'm wondering which patterns others are seeing and what they mean.

Pattern 1:

#
# # 
# # #  
# # # #     
# # # # #   
# # # # # #
# # # # # # #

• Positive explanation: "All good."
• Negative explanation: "Too good to be true. What's really going on?"

Pattern 2:

#
#
# #
# #     
# # #   # 
# # #   # #
# # # # # # #

• Positive explanation: "This was way easier than we thought, let's pull in more stories."
• Negative explanation: ??

Pattern 3:

#
# # # #
# # # #  
# # # #     
# # # # #   
# # # # # #
# # # # # # #

• Positive explanation: "Not sure about this work at first, then turns out easier than we thought."
• Negative explanation: "Not enough progress, let's stop writing unit tests to get 'done' on time."

Answer 1

This is recognized around our office as the "Ah, crap! I forgot about that." burndown:

    # # #
    # # # #
    # # # # #
    # # # # # #
#   # # # # # #
# # # # # # # #
# # # # # # # #