Why do people speak of KOing Ultra Necrozma and not catching it?

Question

I've seen several questions about battling Ultra Necrozma, but if that's the case, why does it always say they're trying to kill it, are you not able to catch it even though it's technically a wild Pokemon battle? Please explain, also, is this the same Necrozma fought on Mount Lanakila? And finally, you can get the one on Mount Lanakila pre-E4 correct? The location's available, I'm just not sure if he appears till later. Thanks for all your help in advance!

Comments

I just want to clarify; what in particular is your question?

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My question was what was the reasoning behind/reason for them not being able to catch Ultra Necrozma, and if Necrozma was available pre-E4.

Answer 1

You fight Ultra Necrozma in Ultra Megalopolis, where it cannot be caught and must be fainted. Afterwards, it can be battled and caught in its regular, unfused form in Mt. Lanakila, which can be done before beating the E4.

Comments

Thank you KRLW!