How often does mirage island appear in Sapphire and what Pokemon are there..

Every in-game day, a 5-digit number is randomly generated, ranging from 00000 to 65535. If you have a Pokemon in your party whose ID number matches the randomly generated number, Mirage Island will appear. You can check if you have a match, but not the number itself, by talking to a man in Pacifidlog. It's not worth waiting for it to appear or going out of your way to make it appear. The only Pokemon that can be found there are Wynaut. You can also find the Liechi Berry here, the only place other than events that you can obtain this Berry in the third generation. It's also not worth the trouble, as it only increases Attack when the holder's HP falls below 1/4.

Every in-game day, a 5-digit number is randomly generated, ranging from 00000 to 65535. If you have a Pokemon in your party whose ID number matches the randomly generated number, Mirage Island will appear. You can check if you have a match, but not the number itself, by talking to a man in Pacifidlog. It's not worth waiting for it to appear or going out of your way to make it appear. The only Pokemon that can be found there are Wynaut. You can also find the Liechi Berry here, the only place other than events that you can obtain this Berry in the third generation. It's also not worth the trouble, as it only increases Attack when the holder's HP falls below 1/4.