Can someone tell me if you're able to breed Cosmog?

You can't

no, but you get a 2nd cosmog in the postgame for the other legendary

>>29840932
How many games let you catch the opposite game's legendary? Is this the first time or am I forgetting previous games?

>>29840932
>>29841004
It evolves into the box legend so you can trade for the other one

>>29841004
Gold/Silver also did that.

>>29841004
HGSS

>>29841004
Gold and Silver started it.

>>29841004
HGSS let you catch both

In Emerald you can catch both Kyogre and Groudon but I dont know if that counts

>>29841025
Ah, that's interesting. So is this the first game where you can get two legendaries?

Though do Lunala and Solgaleo count as legendaries if they evolve from cosmog?

>>29841095
Yes. Though they're technically Ultra Beasts. They've just been living in the Pokemon universe for so long people have always thought of them as Pokemon.