So, I think it'd be cool and def increase the value of pets/want to breed if we did a Monthly Pet Species. Cycle them in and out each month, but keep them for future years. So like January would have a special pet and each January the pet makes a return to one of the areas, but Feb-December, the only way to get them would be from breeding/purchasing from other players. Each month would have a special pet species associated with it.

This could be interesting, but I suggest that
Essence of said Species can be found all time
in Diamond Shop, but prices are a bit up when
not in said month of the said pet!~ >:^O

I like this idea, but I think it may be a little difficult to pull off considering the Nurturing system. People would still be able to get the potential Essence drop from eggs and hatchlings of that species throughout the year, regardless of month. o.o

Mhm. The Essence drops are meant to be a little rare, though, ne? I don't think it'd throw it off too much, especially considering that there wouldn't be the offset of the Battle Drop Essences to drive the prices down. That would prob make the actual Essences worth a bit more, too.

I don't know about a monthly pet but maybe a pet for every two or 3 months? Having to add in 12 new pets seems hard, especially considering 11 of them new players might not know about meaning they wouldn't draw in new players. But 6 (2 months each), 4(3 months each), or 3(4 months each) pets doesn't seem to bad. Although perhaps make essence drops for them more rare during off months? Especially if there's only 3 or 4 of them. Also new players might want to wait to join so they can start with them which isn't good either so I'd recommend perhaps not being able to start with them? Only allow creation of them through a special generator?

There would be no worry about using later breeds for starting pets. The game is set up like Pokemon in that respect, and new players are only able to make the first six starting species for a starting pet (which means no Faelora/Bulbori/Morkko starters).