Generally, Scarf Mewtwo is outclassed in what it does by either LO Mewtwo or other Scarfers. As you didn't provide context as to the rest of your team, it's hard for me to concretely suggest a replacement. If you need it as a revenge killer, Genesect, Palkia, or Kyurem-W will work well. As a sweeper/cleaner, you should probably just ditch the scarf and go for straight-up psycho killer Mewtwo. If you could post your team (in hide tags, preferably) I can help a bit more.
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