Can you have 4 Electivire and 4 Electivire Lv.X in the same deck?
No, Lv.X Pokemon are considered the same as other pokemon with the same name. You may only have a maximum of 4 combined in your deck (i.e. 3 Electivire, 1 Electivire Lv.X).
Source: PUI Rules Team (2008-09-25)