Just the sketch, but this is Melody's Crap Hit The Fan form, activated the same way as Voice's. Her arms are two halves of one cannon, put together they form the whole one. Melody's CHTF form is all about Melee. She doesn't have invincible armor, but it's pretty dang strong. The form lasts for about 15 minutes, or until she uses the cannon (either once on full power, or twice on half power), which ever comes first.