Firstly, make sure you have the National Pokedex (if you've seen all the Pokemon in your initial Pokedex, go back to Professor Rown and talk to him). Then wait until night-time. In the Old Chateau, there ought to be a room with a TV in it. Go up to the TV and press A; there is a Lv15 Rotom (Electric/Ghost type) inside. This apparently may take a few goes before Rotom appears, but it worked on the first try for me.
Rotom has the Ability Levitate and the attacks Thundershock, Confuse Ray, Uproar and Double Team, if this helps. It's incredibly easy to catch.
Other than that, I think there are a couple of items in the Old Chateau; nothing too major.
The items are a dusk stone and a charcoal. Use a quick ball by the way.^this is not the same guy. it's a legendary pokemon.
He is in Eterna city. The house one or two houses down from the Pokemon center.
to dig you need to go to eterna city then go to the house that has a sign next to it.
Number 152 it's Rotom you can find it by talking the TV in old chateau (it has to be at night) Old Chateau is in Eterna Forest at the northwest of Floaroma town Hope i helped Source:Brain
Right after you get the National Dex in Sandgem Town. After that he is Eterna City in the southern most house before you leave the city, on the left.
After you get the National Dex, talk to Prof. Oak in a house at Eterna City. He will give you the Up-Grade to evolve Porygon to Porygon2 through a trade.
it is a haunted house in eterna forest hope that helps
Yep. In the abandoned house in Eterna Forest
Talk to an old man in a house in Eterna city
he's in eterna. got a sign in front of his house.
Rotom, He can be found in a flickering tv in one of the back rooms in the haunted house in the Eterna forest.
in the house near the bottom of eterna city Look for them.
He is in Eterna city. The house one or two houses down from the Pokemon center.
to dig you need to go to eterna city then go to the house that has a sign next to it.
If u talking bout underground kit its in a house near the pokemon center in eterna
You go to Eterna city and go the old mans house .I think his house is next to the Pokemon center.
Eterna City And It Is Just Above The Gym (It's A Building) 99Lloyd99
in Eterna city, you will find the Underground Man. he is in his house. Talk to him, and you will get an explorer kit.