I am a somewhat new player to EteRNA, but I know that many bases in a row is unnatural and bad for lab. However, the default base is Adenine, and if I’m like any other players, then I don’t change the loops, and that leaves unnatural. However, it can also be a good thing, since it would take a while to replace all these “null” bases with another base, which could cut down on actually solving the puzzle. Furthermore, there is no such thing as a “null” base in nature (as far as I’m aware), so adenine does seem to be a natural choice. However, it might be nice to have the option to choose to have a base default to a “null” base in the puzzle maker. If this idea has already been considered, or has such obvious downsides that I did not see, I understand.