I have looked into this closely enough and I can confidently say that master-P has the following alts (this may not be an all-inclusive list):

• berserkerbarrage - https://bitcointalk.org/index.php?action=profile;u=367338
• newflesh - https://bitcointalk.org/index.php?action=profile;u=157072
• AccTraderALT - https://bitcointalk.org/index.php?action=profile;u=512520
• IronMarvel - https://bitcointalk.org/index.php?action=profile;u=176914 (not to be confused with IronMarvel2)