Vintage deck (please comment)

You can only use 1 Demonic Tutor in Vintage... Plus i'd drop the Foresee and add 1 Brainstorm,1 Ponder, and 1 Preordain

look good? would diabolic tutors work?

Using the vintage card pool, you might want to cut the diabolic tutors because they cost 4 mana. The tutor effect is nice, but there are other ways to get it. Lim-Dul's vault is essentially tutor, and vampiric tutor would be a good card to run a single copy of (it is restricted). You might want to run a ponder in the place of one of your copies of preordain, it is an incredibly powerful way to search for cards.
Demon of death's gate won't work especially well here, you don't really have a way of getting it in play and it detracts from your combo (e.g. it will be a dead card in your hand).

Sphinx of Jwar isle and Necroskitter essentially have that problem too. You probably want to force out a win in the form of a 20/20 flier as soon as possible. You probably won't get to playing those creatures that you added. Cards in this deck should be rather low in mana cost so you can play them quickly. You want to either search for combo pieces or disrupt your opponent. Duress is an excellent form of disruption in vintage, but you may consider adding more disruption and card draw like that in this deck. Hymn to tourach is an excellent card for that purpose. Another card you might want is gravestorm. You get extra draws unless your opponent continually puts stuff in their graveyard.

One last thing: Try putting in a copy of Urborg, tomb of Yawgmoth. It lets your dark depths tap for mana.

The deck seems much better, but the bad moon still confuses me. If you have the budget, replace it with 3x grim tutor. That will add greater levels of consistency to your deck

I think rhystic tutor could be good in this instance. Consider cutting the walls of frost and some of the bloodghasts for a fourth rhystic tutor and a few copies of frantic search. That card is rather powerful, as it is essentially a free spell and allows you hit combo pieces faster. It was recently unrestricted by the dci. As nice as the walls of frost are, creatures in vintage often have ways of getting around that (Cold-Eyed Selkie, Sphinx of the Steel Wind, Akroma, Triskelion, etc.) Bloodghast seems a little strange because the 4-6 dmg they can get in for in a longer game won't be relevant when you try to finish them with a 20/20. You may want to cut them for spell pierce, which is awesome in this format.

Also, Urborg, Tomb of Yawgmoth is awesome. It lets your dark depths tap for mana, instead of just sitting there. A copy or two in place of a swamps or reflecting pools would be amazing for you.

That means that there can be only one copy of each of them on the field at the same time. A lot of people misunderstand the "legend rule". If two copies of the same legendary permanent are on the field, they destroy each other. This only happens for the same card. You can have a dark depths and an urborg, tomb of yawgmoth on the field and nothing will be destroyed. If you were then to play a 2nd copy of dark depths, then both dark depths would be destroyed. Planeswalkers also follow this rule.