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Cerulean Cave is a large cave located off of Route 24. Surf will be needed to enter the cave, along with defeating the Pokemon League AND giving Celio the two gemstones. Inside are many tough Pokemon, including the strongest Pokemon alive, Mewtwo!
There are plenty of good items and strong pokemon so bring lots of Ultra Balls and your Super Rod. You will need Surf and Rock Smash.
Mewtwo: Level 70
-Psychic- Even if your Pokemon resists psychic, this is a very powerful move that cannot be taken lightly.
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-Recover- 10 PP, stall out it's 10 recovers before trying to catch; this will be a long battle if you decide to save your Masterball for the legendary dogs
-Safeguard- This protects Mewtwo from special conditions, so put it into paralysis/sleep before it can use safeguard.
-Swift- Normal type attack, never misses, so don't rely on lowering accuracy to prevent damage.
Best method of countering Mewtwo is to bring a Sableye, which is found in only in Sapphire, Emerald, and Pokemon XD: Gales of Darkness. It is immune to both of Mewtwo's attacking moves and can deliver super-effective hits such as Shadow Ball or Faint Attack. If you don't have a Sableye, you can could bring a psychic, steel or dark type, as they all resist Mewtwo's strongest attack
