Arceus Plates
Eventually, Nintendo will make Arceus - the Pokemon god - available through a Mystery Event. This amazingly powerful Pokemon can be any type you desire. It just needs to be holding a plate of that particular type (Zap Plate for electric, Spooky plate for ghost, etc.). The only place to find these plates is the Underground. As an added bonus, Arceus plates can be used by other Pokemon as a single-type boost, but if you've readlast week'sPokemusings then you know we think these kinds of hold items are stupid.
Above: Arceus has unlimited potential with its numerous plates, which can only be found in the Underground
Breeding Tools
You can find two vital tools for Pokemon breeding in the Underground: Heart Scales and Everstones. Heart Scales can be used to make a Pokemon remember a move it forgot. This is useful if you received a Pokemon in a trade and it doesn't have some moves you need. You can give a Heart Scale to the Move Relearner in Pastoria City so that he can re-teach old moves to your Pokemon. There are also some cases where a Pokemon can only learn level-up moves gained through evolution with the help of the Move Relearner. Everstones are also bountiful in the Underground. These are useful for getting the right nature for any new Pokemon you breed. For example, an Adamant female Charizard holding an Everstone has a high chance of producing an Adamant Charmander.
Big Money
Spending time digging in the Underground will increase your riches. Rare Bones and Star Pieces are two items that exist only to be sold at high prices. You can also sell some extra treasure whenever you need cash. There are currently 67 Water Stones in our backpack. We'll never need that many, but if we're ever short on cash we can sell some at the local PokeMart for 1,050 a pop.
Trade Bait
All the treasure you find in the Underground should be used to make your GTS offerings more attractive. You should always attach an item to any Pokemon you put on GTS. Say someone is looking for a level one Chikorita. There could be six available, but only yours is holding Sun Stone. Naturally, yours is the most likely to get snatched up.
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