Fine, "heavily inspired by".

Using the direct sprite data would have been a massive IP violation

Drawing something similar can surely have people questioning it, but it might be sufficiently different to (try to) avoid bigger complaints.

Not massive at all. The pipes are not a substantial creative artifact in their own right.

An IP violation would require causing brand confusion or drawing sales away from the original

You're thinking of trademark, which would require confusion.

Copyright is another type of IP, and does not require confusion. It only requires copied content.

I don't think the creator of flappy bird gave a damn about IP violations.

maybe from a different Mario game?

Looks a lot like Mario Advance 3.

Super Mario Advance 3 was a port of Yoshi's Island. Yoshi's Island pipes for reference:

http://protipoftheday.com/sites/default/files/yoshis_island_...

Not anywhere close.

Actually I was thinking of Super Mario Advance 4, which is the port of Super Mario Bros. 3, thus the mistake on my part.