How to Unlock Nya - Monster Rancher 1
Nya is the easiest monster to unlock in Monster Rancher 1, really the only thing required of you to unlock this monster is to play the game for 40~ hours. The first thing you need to do in order to unlock Nya is visit the Item Shop at the start of the game, this will trigger a hidden timer. Once this timer is triggered you have to wait 25 ingame years before you'll get a notice from the Item Shop about a new item in stock - a Cat Doll.
In order to unlock Nya as quickly as possible you'll want to visit the Item Shop very early on at the start of the game. However, you probably won't read this guide until after you've started the game and visited the Item Shop which means this advice is probably not going to be too helpful for you.
Once the Cat Doll item is finally for sale in the Item Shop head there and buy it for 1000G or when it's on sale for less. All you need to do after purchasing this item is to take it to the Lab and use it when Combining 2 monsters. It doesn't matter what monsters you use in the Combine process, the result will always be a Nya monster.
As always, once you unlock Nya you'll be able to start getting them from Discs that you use at the Shrine as well.
How to Unlock Nya Monster:
1. Visit the Item Shop at the start of the game
2. Wait 25 in-game years
3. Combine any 2 monsters and use the Cat Doll item to create a Nya