Why does this have two mana abilities?

Technically, it doesn't, which is odd. Since the Primeval Forest isn't a "Land - Forest", it doesn't add green to your mana pool, and the reminder text is just kind of floating about and not doing anything. Did you intend this to be a Forest, Camruth? I'm not sure which accident you made, since you have a line about requiring a 'basic forest' for the second ability to work... which still works if this is a non-basic Forest, but I wouldn't expect an ability on a non-basic Forest to ask for a basic Forest. That, and the fact that this card is insanely broken if you can just tap it for green mana.

Because in the original draft it was a Land - Forest and when I decided it made it too strong I forgot to remove the : Add cause I'm thick sometimes :-O Plus it is a work in progress and still needs work balancing it.

Yeah, that's much more sane. It's still probably too strong, mind you, but at least it isn't "OMG! Play 4! Play 4!"

At least its not Gaea's Cradle powerful :-)

Can't you just replace "Primeval Forest has Hexproof as long as you control a basic forest" with hexproof, considering the final clause?

Why does a land need hexproof, anyway?

I was going to make it Indestructible but Indestructible has been done before so I thought I'd try something a little different.
Hexproof prevents opponents from doing anything bad to it unless they take out your Forests (which kills this anyway).
The original 'theme' was that to get to the ancient heart this represents you had to get through all the surrounding forest.

Interesting. Unfortunately way too good; "need to have a Forest" isn't anywhere near enough drawback on a land that taps for two mana. I'm not sure it's even enough to stop monoblue decks playing it along with Breeding Pool purely for the acceleration, like monored Goblin decks played Pendelhaven.

Hexproof is useful on a two-mana land; most of my decks have some of the Ravblock karoos in (Boros Garrison etc), and they're always the first targets for Vedalken Plotter or whatever. Perhaps with the "ETB bounce a land" this could be fair.

Knowing Wizards policy on Mythics, I'd expect to see this card sometime soon:

Primeval Forest
Land - Forest
Mythic
­: Add to your mana pool.
Whenever Primeval Forest enters the battlefield or attacks, you may search your library for up to two land cards, put them onto the battlefield tapped, then shuffle your library.

OK added the bounce a land clause - which I had been considering myself so hopefully this should be OK now.