I hate my friend. Today, while I was watching him dig he found 3 ODD KEYSTONES. One in Sunnyshore, one in Newmoon Island and one in the PL. He also finds fossils like crazy.

I haven't found a single keystone and only 2 fossils. (Skull and Helix)

I dig up a bunch of Revives tough. One time I had 2 in the same time!

sorry for being semi-off topic, but what is so great about odd keystones? don't you only need one to fix the tower and you're done?

Okay, I usually find alot of Odd Keystones too. They are what you need to get Spiritomb, (and they are one of the rarest treasures, so if you find them, it's awesome). Maybe there is just a better chance to find certain items on a certain day or at a certain time of day. I found about 7 different Plates in the Underground in an hour. Another time, I found Fossils really easily and quickly. Altogether from that day, I had found about 30 fossils (eg. Old Amber, Helix, Skull).

The most common (and actually quite useful) things I find in the Underground are Fire Stones and Thunder Stones. They come in useful sometimes. Maybe when I catch another pikachu, I'll evolve it for pokedex sake. If I get more than 14 Fire or Thunder Stones, I usually sell some of them for good cash. But I keep the stones I find just in case they come in handy.

The best things I have found are a Water Stone (which I used to get my current Vaporeon,) a Moon Stone (which I have not used, can't decide if I want a Clefable, Delcatty, or Nidoqueen (I might go for Nidoqueen.)) I'm hoping to find more one day. Another awesome thing I found was an Old Amber. Aerodactyl rocks. Another cool thing I found was a Max Revive (which I unfortunately used.)

Mine has got to be thunderstones, i have had 40 at one time.

-Palindrome-

I find heaps of heart scales, still unsure of their use in the game. The only fossil I have found was on Platnium, turned it inot a cranidos which I traded fr a psyduck as to evolve my machoke or was it my kadabra, not sure. Still haven't found anything of use as yet.

heartscales are used to have pokemon remember moves they can learn at earlier levels. you give them to the move remember in pastoria city.

I have just found my first ever heart scale underground, never came across any for some reason

-Palindrome-

Ones i always get were Water stones O_o and then i had to sell half of them ( I had 60 of them O_O)
The rarest ones i get were Rare BOnes (for money)

the rarest thing ive found is a mew hair .dont make it to a pokemon though .it will be disstroyed. iv found over 50 fossils though

most common thing? all shards EXCEPT blue, hard stones and water stones.

very frustrating.

Most common Underground Items?
It's been about a year since I've been to the Underground, but I know I have a whole box full of Cranidos. Oh, half a box full of Anorith, while the other half being the odd Kabuto and Lileep. Ooh! I forgot about my three Aerodactyls! Yeah, that makes it like at least 40 fossils regenerated. I still have like 20 of each fossil (except root and dome- 5 and 4 respectively).
Second-most found?
Well, I'd have to say Heart Scales. I have 34 of them right now, which is ridiculous!
Rarest?
Definitely Dusk Stones, Plates, and Water Stones. I only have 5 water stones, and one Dusk Stone (I had two, but I used one to get a Honchkrow)
So yeah. (Man, So yeah/ is becoming my catchphrase these days!)
~torchie13125

Most common thing I've found underground: Spheres. I actually try to avoid digging up those things. Got plenty buried all over the place.

Though if you're talking items you can use outside the underground: Waterstone. Dunno why, but I have well over 80 last I checked.

The best thing I've ever discovered underground: Heartscale. I've only ever found about 35 of these. I want more.

The most common thing I uncovered in the Sinnoh Underground would be...either the Fire Stone, Moon Stone or the Thunder Stone then again I am not really sure exactly what it was...meh...