What is your opinion on this deck, and what do you think could make it better? Thanks in advance.

Creatures:
4x Dark Confidant
2x Snapcaster Mage
4x Tarmogoyf

Spells:
2x Abrupt Decay
1x Ancestral Recall
1x Brainstorm
1x Dismember
2x Flusterstorm
4x Force of Will
1x Mana Drain
4x Mental Misstep
1x Steel Sabotage
1x Demonic Tutor
1x Ponder
4x Preordain
1x Time Walk
2x Jace, the Mind Sculptor
2x Sylvan Library

Mana sources:
1x Island
1x Library of Alexandria
4x Misty Rainforest
1x Polluted Delta
2x Scalding Tarn
1x Strip Mine
2x Tropical Island
3x Underground Sea
1x Black Lotus
1x Mox Emerald
1x Mox Jet
1x Mox Pearl
1x Mox Ruby
1x Mox Sapphire
1x Sol Ring

Sideboard:
1x Abrupt Decay
1x Dread of Night
1x Energy Flux
1x Forest
3x Grafdigger's Cage
3x Nature's Claim
2x Nihil Spellbomb
2x Null Rod
1x Thrun, the Last Troll

Run monastery mentor!

This deck is very fair, and I think that it would struggle as a result. Given that it is bug, I would expect to see some Leovald, or deathrite shaman. The mana base feels very tight too. Dark Confidant versus delve spells is a very hard choice. I love Bob, but the delve spells are really good.

I'm not sure Mentor makes a lot of sense as a suggestion here.

The list you have is very similar to the BUG or BugFish archetype in Vintage. BUG runs a lot of the same cards you are, and usually leverages:

• Deathrite Shaman (which is very useful against the mana denial strategies which are common in vintage)
• Leovold, Emissary of Trest (which is a strong hoser against blue decks centered around cantrips and draw spells)
• Some BUG lists also take advantage of the one-two punch of Wasteland + Null Rod, but that's not entirely necessary

I'd highly reccomend you check out this excellent primer by @JonHammack http://themanadrain.com/topic/1323/dr-shaman-or-how-i-learned-to-stop-worrying-and-love-the-bug-r

That's a version of the deck with a red splash. You don't need the red splash to compete, but it's worth reading just to get an idea for some of the other cards people have played in similar decks

I was running 4 deathrite, but they honestly felt like a waste of space. I don't think this deck runs enough instant + sorcery to make use of his, and he just feel like a mana dork that could potentially have no lands in the grave, and mana dorks don't seem great in modern to begin with. Maybe I'm just wrong, but it feels better without them. Leovold could be good, what would come out for him?

-2 goyf
+2 leovald

I'd also suggest a toxic deluge in the board.

I built BUG as a side project in Vintage. 15 proxies makes the venture rather easy. I find the deck rewarding, and while I normally play Shops, I would describe BUG as a more interactive build that has a small but interesting fanbase. The natural idea evolved from legacy builds, but I really didn't pull the trigger until I was Jeremy beaver pilot a BUG build with Managorger Hydra in it into a T8 at a recent EE Vintage event. Managorger is interesting because it has natural applications against shops, which have a hard time removing one, and other blue decks, who often churn out enough CA to make the Hydra huge really quickly. In all of this I understand that Hydra is a fringe choice at best, and if you are still reading this you are probably scoffing at the idea of even considering the card. This is fine, it is just how I like playing the deck, you will find several deviations from the norm in my deck, but I enjoy it. Some takeaway you can gather regardless of build:

1-2 Null Rods Main
2-3 Leovold
2+ DRS

My build:

3 Leovold, Emissary of Trest
3 Managorger Hydra
3 Deathrite Shaman
2 Trygon Predator
1 Notion Thief
4 Force of Will
3 Preordain
3 Mental Misstep
1 Ancestral Recall
1 Stifle
1 Misdirection
1 Mindbreak Trap
1 Time Walk
1 Treasure Cruise
1 Gush
1 Ponder
1 Brainstorm
1 Dig Through Time
3 Abrupt Decay
1 Demonic Tutor
1 Jace, the Mind Sculptor
2 Null Rod
1 Black Lotus
1 Mox Emerald
1 Mox Sapphire
1 Mox Jet
4 Misty Rainforest
3 Polluted Delta
3 Tropical Island
3 Underground Sea
2 Island
1 Forest
1 Strip Mine

SB

3 Nature's Claim
2 Tormod's Crypt
2 Yixlid Jailer
2 Virulent Plague
1 Snuff Out
1 Dismember
1 Mindbreak Trap
1 Flusterstorm
1 Grafdigger's Cage
1 Ravenous Trap

I think that if you cut Dark Confidant for delve spells you should have some number of jace, vryn's prodigy.
I really like the sylvan librarys though. I am never sad to see that card.
Edit: Also throw in 1 gitaxian probe for good measure

A minor nitpick – I think you're going to be pretty disappointed by the Thrun in the sideboard. The uncounterability doesn't really matter, as most decks with counters wouldn't really consider a 4/4 with no evasion a threat worth dealing with. Workshop and Eldrazi decks might have trouble dealing with a large regenerating blocker, but at that mana cost it might be very difficult to cast it against them. That's the only card in your list that immediately stands out as underwhelming.

I've been playing BUG for the past few weeks and am overall happy with the performance.

• I have made adjustments with included the removal of Dark Confidant. I love this card but he was not good enough and was doing far too much damage to me.

• The two all stars in the deck are Leovold and Ramunap Excavator. Ramunap works best if you plan on building a mana control build like I have built. This with null rod and recuring wasteland/strip mine/ghost quarter works great. If you land a fastbond, you really can take over the game with this guy.

• Your list looks more aggressive which is not a bad route. I have 2 delvers in my list that really come in handy when you need to have quick or flying damage. Your list might make good use of this if you are looking for speed.

• Dismember has not been very impressive for me. I have one in my sideboard for the eldrazi matches but otherwise, abrupt decay is almost always better.

• I personally don't like having more than one Sylvan Library. I would replace the second one with gush.

• For me, BUG lists play the aggressor. As such, I rarely get good use out of Library of Alexandria as I play my spells quickly. This is a tempo deck so I think you would get more out of a wasteland (or 4).

That's my BUG philosophy. Hope it helps.