Despite increasing evidence that I'm the only person who reads this thread, I've decided to make a brief guide to my favorite hero, dark seer:
What are dark seer's skills?
http://dota2.gamepedia.com/Dark_SeerWhat role does dark seer fill?
Dark seer is a solo offlaner who uses ion shell to last hit from a safe distance with ion shell while making it difficult for the enemy carry to farm, and can escape from ganks with surge. While his skills don't scale particularly well with farm, he can use the gold he gets to buy important utility items for his team.
So how do I play dark seer?
First, you're going to want to make sure that you get the offlane to yourself. Ion shell will push the lane hard, making it difficult for your lane partner to last hit, sometimes even to survive.
Next, you're going to want to buy a stout shield, a set of tangos, a healing salve, and a soul ring recipe, then head to the offlane. Then you'll want to figure out how many people you're laning against. Usually it will be 2-3, and if that's the case, wait until your creep wave is about to reach theirs, then put an ion shell on the melee creep that's 2nd or 3rd in line. The front creep will take aggro and die first, and the ranged creep won't get close enough to do anything with the shell. However, if you're laning against a single opponent, ion shell yourself, then stand in the middle of the enemy creep wave. If the enemy approaches, move towards them and right click them. If they don't, focus on last hitting.
Now I'll talk about skill and item builds. For skill build, you're going to want to max ion shell first, leveling it at 1, 3, 5, and 7, while getting surge at level 2 and possibly 4 if you think your opponents have that much kill potential. After that, put all your points into vacuum. Your ultimate is a tricky thing. Since it's pretty ineffective until you have several points in vacuum, you don't want to get it too early. I usually go for it after I have 3-4 points in vac, but I've heard a lot of different opinions on the subject. The item build is pretty simple. You want to build soul ring first, then boots. I personally prefer tranquil boots, but it's perfectly acceptable to build arcane boots or simply stick with the basic boots. After that, buy a magic stick, which you can upgrade to a wand if you want (I usually don't because I'm trying to rush mek), then buy a mekansm. From there, you can go for any number of items, depending on what you and your opponents are playing. Pipe of Insight and Shiva's Guard are strong in teamfights if your opponents have a lot of physical or magical damage, and Black King Bar can be an OK choice some games. You could also go for a blink dagger to better use your wombo combo, or a scythe of vyse to lock down an enemy. An aghanim's scepter can be nice lategame, but since it's much stronger lategame, it's probably a bad choice to build early.
So, now that that's out of the way, let's go back to the game. You were ion shelling creep waves to last hit, right? Well, by now you probably have your soul ring and boots, so you can try "creep cutting". What you're going to want to do is ion shell yourself, go around behind their tower through the jungle, and get the enemy creep wave to start following you before it even reaches their tower. Then you're going to want to run, because this is the perfect opportunity for the enemy team to kill you. Once the enemy heroes stop chasing you, position yourself in the middle of the enemy creep wave and burn it out with ion shell. This guarantees you all the last hits, and forces the enemy heroes to tank your (probably ion shelled) creep wave under their own tower.
There are some offlane heroes that just want to get a couple of levels and brown boots, then go around ganking lanes. Dark Seer isn't one of them. Unless they're diving your teammates under tower, you probably want to stay in lane until you get your mekansm, 3-4 points in vac, and at least one point in wall of replica. Once you have those, though, you want to start grouping up with your team and pushing a lane. The early mek should give your team a huge advantage. Keep 5manning until you win the game.
What are some tips and tricks for dark seer?
-Remember to use your buffs on your teammates. A timely surge on an ally can secure a kill or save a life, and ion shelling your melee carry can give some good damage.
-Vacuum has a ridiculous cooldown, don't use it lightly.
-Your base damage and armor are both pretty high, so you can trade hits with most heroes at level 1.