Lets stop beating around the bush. Do you want a dirt jumper? or do you want a trail bike? Its one or the other, nothing in between, they dont even compare in similarity.
Dirt/Park: Is going to have short chainstays, long top tubes, short seat tubes, horizontil dropouts, integrated headset, and going to be steel, and either very expensive or heavy. Put a cheap sh1t dart fork or something on it and your going to need a very good dentist and new wrists.
XC trail: Gears obviously, not gonna get sliding dropouts for $800, if you do they will slide right off the bike. Geometry will be opposite of a DJ/park frame. Go huck yourself off a set of stairs on an aluminum xc/ht frame and let me know how your ankles feel. and the chain is gonna be flailing all over the place. Go full suspension in that price range and your buying a boat anchor with wheels.
Your need to be more specific and state exactly what/where you want to do and your ability. If your 15 years old and still pooping zits onto the mirror you will need a different bike than say a 200lb midage cubical jockey who wants to jump off the loading dock in raritan center.