Ayu-mi-x II Version Non-Stop Mega Mix was created on 2000-03-29.
Ayu-mi-x III Non-Stop Mega Mix Version was created on 2001-02-28.
Yes there is a mega version of every weapon excluding the wrench which you can upgrade at vending machines throughout the game.
Mega Twins was created in 1990.
Mega - magazine - was created in 1992.
Mega Force was created in 1989.
Mega Power was created in 1993.
Mega-Carrier was created in 2005.
Mega Brands was created in 1967.
Mega Zone was created in 1989.
Mega Maldives was created in 2010.
Mega Zeph was created in 2000.
Mega Turrican was created in 1993.