Gen VI:
Additional effects such as trapping from moves like Fire Spin and Attack reduction from a burn are not prevented. If paralyzed, a Pokémon with Magic Guard will suffer from the normal Speed reduction but cannot be fully paralyzed.
Gen V:
>Magic Guard no longer grants immunity to being fully paralyzed
So in the Gen V battle mechanics, Alakazam (or any other Pokemon with this ability) will get parahaxed/ immobilised like any other Pokemon.
Magic Guard