It seems it's new trend on Japanese Tweeter. Depends on number of retweets, user will draw/reveal something. Here's Mashima's list:
TL:
1 RT - my work enviroment
4 RT - first character I practised to draw in my life
5 RT - complete set of reference data
8 RT - one small technic I use when I draw
12 RT - I'll do my best drawing erotic picture
What will I do if I get 12 RT...
"This is my working place. Too bad, that the place where keyboard lays is so small, but I got used to it. The paint tool I'm using is SAI"
"First character I practised to draw was
Kinnikuman. There are too many of references data to show them all. I always have 3 volumes laying on my desk."
"Small technic would be something like this I think, I've been using such faces, but practically I don't use them anymore. I'll leave erotic pic for another day!"
As for Lucy faces: normal, no idea, no idea, normal 2, dark brown/tanned, yellow, Lucy, Gajeel, Erza.