What You Need to Know
Intro- Dark Seer. As a support and a pusher Dark Seer has great qualities to benefit your team as well as yourself. Naturally as a support hero Dark Seer benefits from team work and good communication. A support hero is quite useless if you or a good amount of your team are not team players or not interested in working together. In this guide I will show you how I play Dark Seer and be successful simultaneously.
Skill Info-1Q.Vacuum - This ability is your most important ability, especially in team fighting scenarios. This ability allows you to bring enemies together, closer to your team or further from your team.
-2W.Ion Shell - This ability is what makes Dark Seer a great pusher and early power-house. Throwing this ability on ally melee creeps will allow a huge advantage in lane pushing as well as harass any and all heroes nearby the affected creep. This is also a great use of insurance in a team fight. Putting this ability on yourself or an ally hero who is in the heart of the fight will produce a ton of damage and scare off a team, allowing for your team to pick off the slower runners.
-3E. Surge - This ability increases the target's movement speed by MAXIMUM, highly useful skill that when used can allow you or an ally to escape or chase down victim enemy heroes. As a support in a fight this is best used on an initiator to ensure a fight or chase down a weak enemy hero. Surge is best used on carry heroes allowing them to pick up kills or get them to where they need to be as a general map position.
-4R. Wall of Replica - This ability is fairly useful; however, I (as many others do) focus on maxing Vacuum and Ion Shell first for great pushing and team fighting. This ability is very useful in team fights for adding additional ally targets as well as the replicas dealing damage to enemies at your control.
Summary-Dark Seer is a versatile support and should be played to better the team and push lanes at opportune moments, his play style is fairly straight-forward and is pretty easy to pick up. Keep in mind Dark Seer is a melee intelligence hero and can be picked off early if you are not careful. Keep Observer Wards up for rune domination as well as visual aid against or for ganking. He is built with active items and all active abilities so make sure you pay attention to both.
Vanguard - I build this item ASAP because it makes for excellent survivability and allows you to tank some fights in which you will be singled out.
Urn of Shadows - In my opinion core for almost all support heroes. Being able to use dead enemy heroes to heal your team is invaluable for pushing and closing the gap that is returning to base.
Observer Ward - Warding as a support is almost always your job, warding is one of if not the most important aspect in DotA, vision of the enemy and runes is key for victory. Can be replaced with Sentry Wards.
Town Portal Scroll - Buy them as you need them, a pusher values teleportation.
Extension of Core:
Aghanim's Scepter - A good choice for Dark Seer in general, but I only tend to grab this if my team is doing particularly well and victory is rather imminent.