Well, well, well. Another day in the DL and Genevieve has to face some sort of...cat thing. No matter. Genevieve has plenty to bring to the table. First is her Indiscriminate, which has overkill magic damage of multiple types. Not enough for you? She also has a good physical with Contaminate Energy if Mewtwo doesn't Barrier. Either way she'll quickly bring Mewtwo's HP into the danger zone. If Mewtwo tries to Recover, he'll be locked in a heal loop until he dies or runs out of PP. If he goes for an all out offensive strategy he won't get past Genevieve's solid HP score before being ground into dust. And of course there's always Heal to be contended with if she takes too much damage. There's no shame in losing to such a powerful Undead, and there's no shame in bowing out in Week 2. Hopefully Mewtwo will recognize that when he loses!
