Latios can Mega Evolve into Mega Latios if it is holding a Latiosite.
Despite not being a commonly seen Pokémon, Mega Latios resides in the Overused (OU) tier of competitive battling by virtue of its base form receiving enough usage to be in OU. Mega Latios has better defenses than base form Latios, but it is weaker than Life Orb Latios and faces immense competition from many other Mega Pokémon. As a result, Mega Latios is unviable in OU due to the huge opportunity cost of taking a Mega slot and being outclassed by regular Latios.
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