How exactly does the auto pricer work?
And... about the trophy for my profile, does it go away when I stop paying?
Does the 20 Percent Discount Card last forever? Or just until I am no longer a paying account?
And... What do these items do? Enchanted Hypnosis Wand Tranquil Arcrystal Solid Arcrystal Corrupted Arcrystal Miracle Potion Miracle Potion II
The autopricer can be used once a day, and it prices your items for you at the lowest current selling price.
You get to keep the trophy forever.
The Discount Cards are multiple use. You do not have to have a Gold Account to use one.
As for item uses:
Enchanted Hypnosis Wand - Lets you rename a pet, one time use Tranquil Arcrystal - I think it's wearable? Solid Arcrystal - I think it's wearable? Corrupted Arcrystal - I think it's wearable? Miracle Potion - Changes your pet's color while keeping the species Miracle Potion II - Changes your pet's species while keeping the color
The autopricer only prices items under 1M as well. so if they've price is over that they wont be priced!

The auto-pricer basically gives you the option to price your item at the Lowest current shop price, or the average shop price.
No, you keep the trophy :)
I don't think discount cards are associated with Gold Accounts, so it lasts as long as you have it in your inventory.
4a: Enchanted Hypnosis Wand : Changes a Pet's Name b: The Arcrystals are stat boosters, I think.
EDIT: Ugh, beaten.
So... about those Miracle Potions... Do I get to pick whatever color/pet i want?
Yep, you use it and it gives you a drop down menu of the colors or species currently available for the pet you are using it on. ^^
[edit]
The Arcrystals are wearable, they also combine individually with Ancient Achi Runestone to create minions.
From what I can tell they are not stat boosters, but someone at the Battle Forum might know for sure.