there is no rule saying it has to be in the correct attribute, it can be in any attribute, it doesn't matter, they are all the same(excluding the traps attributes and the bakugan's g's)
I was kind of confused when I read this so I'll re type it...The attributes aren't limited to what the characters use in the show, the packs just give you the character's guardian Bakugan and their trap. I've seen an Aquos version of Spectra's pack, which means it included Aquos Helios (I didn't take notice to if it was Viper or not) and Aquos Metalfencer.