Masquerian from Mysterious Treasures
Against some decks, this is quite the scary card to face against, to be honest.
A deck that uses Water pokemon will find themselves hurting whenever you use Swirling Ripple. How common is that? Empoleon is a rather popular card at the moment. Feraligatr has also been seeing some attention, and might be played. Don't forget the Latios from Lati-lock will be water type as well. Finally, Altaria EX d, and Mew * d are both water type.
Thus, you'll find Swirling Ripples to be an interesting tech option in a grass deck that can fit Masquerian in, except for a few problems... The largest problem comes from the fact that... Most grass pokemon already have water resistance anyways. As far as tech options go, this doesn't seem to be the best idea possible.
So what else can this card be used for? Well, we now turn to his first attack, Centrifugal Force. This attack is quite interesting, but also hard to make reliable. Should your opponent play a pokemon with high retreat cost, such as Magmortar or Electivire, then this attack deals devastating damage for the cheep cost of only two energy. Of course, pokemon with low retreat cost (such as Infernape and Delcatty EX) are also widespread.
The question then comes, can Centrifugal force be used reliably? In a deck focused around Ariados, yes. You're ensuring that the opponent will take 40+ damage if you have two Ariados out, which is not too difficult. Now in a deck not centered around that combo? No.
For the last attack that Masquerain will be seeing use of, is the attack of Surskit. You'll find this attack quite useful before evolving, and even a Memory Berry will surprise you, since this is a free Pokemon Reversal. The ability to pick any pokemon off the bench, and place them active and asleep is incredible in this deck. Should your opponent's only water type be active, you might wish to drag up a new pokemon to avoid losing the Swirling Ripples condition. Perhaps they have a high retreat cost pokemon on the bench? Perhaps you see a power (like Delcatty PK) on the bench to shut off? A highly useful ability, only weakened by the fact that you need one grass energy to use this attack.
And now that attacks have been looked at, let's see how this card works defensively.
First off, his free retreat cost is something that would ordinarilly be seen as a blessing. Why ordinarilly, rather then always? In a deck comboing with Ariados, the Ariados will increase everyone's retreat cost (including your own Masquerain). Therefore, ideally, you won't be able to use the free retreat cost, which is a shame.
Secondly, resistance to a common type (Fighting) is rather useful. Mario decks for instance, can't touch him with their Machops, and are incapable of one shot knocking out Masquerain with any attacks unless a Holon FF energy is attached. Also, Rampardos is fighting type, and has been seeing attention. Rampardos, which his second attack will instantly knock out Masquerian, is weak to Grass type, and is commonly paired with Empoleon. Those last two factors make encounters with him rather enjoyable for the Masquerain player.
Finally, weakness to fire. In this case, the weakness is almost negligable. The majority of fire type pokemon will already be dealing 80 to 150 damage (see Gardevoir EX d, Magmortar, Infernape). Considering Masquerian's HP, the weakness does not accelerate his demise noticeably (unlike pokemon who have 130 HP and +30 lightning weakness). Therefore, it's not too devastating to have fire weakness. In fact, it's preferable to have fire weakness to a type such as Lighting, as there are multiple Lightning attacks that deal around 60 damage (namely Electivire's Giga Impact and Raichu's Explosive Thunder), and would benefit from the weakness damage boost.
Considering all of those traits about Masquerian, it's safe to assume the following.
1) He's not the ideal tech to splash into any deck
2) Masquerian is however, quite capable of surviving in certain decks
3) When the deck is built to take advantage of Masquerain, he is effective at dealing damage, and can throw off the opponent via use of the basic's attack.
Therefore, rating for Modified Format (HP->MT) would be a 5/10. Above average, but enough gaps in it's strengths to make it not too impressive.