This is one of the few cards that is playable in the DP set (Dusknoir being another notable one). Although Magnezone decks have had its own share of the limelight in the metagame a few sets back (mainly because of the sheer versatility of the Magnezones), it has difficulty competing with the faster decks of the current format. Being a stage 2 does not help it's case.
It's HP at 120 is nice for a Stage 2 and since it is a Metal-type, it can abuse Special Metals to make it more tankish. Weakness is fire is very bad due to Blaziken FB, Magmortar SV, and Infernape 4. Resistance to psychic is very much appreciated. It has a huge retreat cost but will not concern you much if it's Poke-Body is in use. If you are attacking with this guy, chances are it has a Metal Energy attached to it, nullifying the expensive Retreat Cost (and can be a great help to its teammates if the need arises). It's attack is nifty and really wants you to attach Special Metals to this one to make it not only tankish, but also an offensive force that should be watched out for. Unfortunately, Grind-like attacks have limited use in this format, especially since the trend is to attack with as few energies as possible. However, it is a slightly viable strategy for Magnezone because it has its own way of energy acceleration (with the help of the other Magnezones).
Once, I had to opportunity to battle someone using this Magnezone and Nidoqueen. The Magnezone managed to have 4 Special Metals on it and with the aid of the Level X, provided free retreat across the board, even to Nidoqueen. Maternal Comfort really increased the tankishness and free retreat to everyone is just annoying.
Usually, this Magnezone is considered for the Level X due to it granting free retreat (which is very appreciated due to the amount of bench manipulation taking place in the format). However, aside from that, it does not offer much. With the arrival of Flygon (RR), free retreat can also be attained without really worrying about how tight the Magnezone lines are already in themselves.
All the Magnezones have their uses and very much have synergy with each other. The problem is, the decks to slow and the weakness really screws it over in terms of ability to tank. If you ever run this outside of Magnezone decks, just run Flygon. At the very least, the dragon has more versatile attacks.
Modified- 7/10 (a nice card, but Flygon is a nice alternative if you find it hard to run too many different Magnezones)
Limited- 8.5/10 (great here with the nice HP and and the attack to abuse metal energies)