Megamind uses his Dehydration Gun on the Go Fish Gang, but not the Doom Syndicate. Why? If you've watched the first movie, you'll remember that without an opponent like Metro Man, Megamind thinks Victory Is Boring. Thus, if Megamind blasted them with the Dehydration Gun so easily, he would experience no thrill.
Then why did he try to capture them all at once with the malfunctioning Brain Bot's Tractor Beam prison?
There is a lot of Continuity Snarl between this movie and the original movie, with Megamind being allies with the Doom Syndicate despite it being told that he's spent most of his life without Minion/Chum, as well as Machiavillain having taught Megamind all he needs to know about villainy despite the first movie showing that his prison inmates teaching him. But if you think about it further, this isn't a Retcon, because:
Megamind stated that he spent most of his life alone, so he was part of the Doom Syndicate for a shorter period of his life.
Megamind's prison inmates didn't teach him all about villainy, they just let him take his first steps in villainy. Machiavillain, on the other hand, taught Megamind the rest of the steps in villainy.
