Tips

• Bloodrage can be cast on creep-hero units like Brewmaster's Primal Split Brewlings, Lone Druid's Spirit Bear, Visage's Familiars, or Warlock's Golem.
• Bloodrage's spell amplification increases damage done by items as well.
• Blood Rite provides ground vision around its AoE.
• Enemies can't easily use Blink Dagger if they're Ruptured. It has a pretty long cast range and the debuff lasts a ridiculously long time, so it can be useful to mess with Blinks from an initiator like Tidehunter or Magnus before a team fight begins.
• Agh's Shard for the "Sanguivore" innate provides a barrier for all sources of self-heals that put you over 100% HP. This includes heals from lifesteal items like Mask of Madness or Satanic.
  • Dagon's active instakills any non-ancient creep. Dagon also heals the caster for a percentage of the damage dealt, which, for an instakill, is equal to the current HP of the creep. You could theoretically Dagon full HP creeps for the overheal barrier with Agh's Shard "Sanguivore".
• If you take the "2 Rupture charges" talent, be aware that multiple casts of Rupture don't stack on the same target, it'll just refresh the duration. What'd you expect, they'll bleed twice as hard? C'mon now.

Counters

• TP scroll. Seriously. Just TP out if he's ganking you. None of his spells have stuns/roots/leashes to cancel it.
• If you can exceed more than 1300 range in one server tick, Rupture won't damage you. This is why you don't take damage from Rupture after TPing back to base, but this is also relevant if you're playing Queen of Pain (move immediately after Blinking max range and you won't take Rupture damage) or have cast range increasing abilities on Blink Dagger.
• The lifesteal Bloodseeker gains from his Sanguivore innate can be reduced by heal manipulation debuffs:
  • Items that can reduce all heals: Spirit Vessel, Orb of Frost/Corrosion, Skadi, Shiva's Guard, and the "Crippling Crossbow" neutral item artifact.
  • Spells that can reduce all heals: Ancient Apparition's Ice Blast, Doom's Doom, Dragon Knight's "Frost Dragon" facet, Drow Ranger's Agh's Scepter Hypothermia, and a few others.
• Bloodseeker's Sanguivore innate healing and Thirst passive can be disabled by Breaks.
• Blade Mail can be good if you're tanky, especially if he Ruptures you.
• Lotus Orb can provide a lot of value when placed on your carry since BS will feel uneasy about initiating a team fight with Rupture.
• Kiss juking goodbye if there's a Bloodseeker on the enemy team. Once a match you'll find yourself wondering, "HOW DID THEY KNOW I WAS THERE???" Then you'll look up and realize that Bloodseeker was giving his team global vision of your ass when you're under 25% HP thanks to his Thirst passive.
  • Thirst vision provides true sight as well. Not even invisibility will save you at critical HP.
• Be extremely careful when jungling at low HP against an enemy Bloodseeker. If he detects you with Thirst vision, you can be sure that his whole team will be quickly converging on your location to score a kill.
• If Bloodseeker has an Agh's Shard, the overheal barrier can be dispelled off with spells like Enchantress's Enchant, Oracle's Fortune's End, Shadow Demon's Demonic Purge, or items like Nullifier or Eul's Scepter.