role: venomancer is a powerful damage per second (DPS) dealer that can support , offlane or even mid, he is a very good lane support and a ganker, and he can offlane just fine using his , and mid depending on the enemies mid hero.
best combo: venom has an op poison and slow, so his best combos should make use of his dps or of his slow (aa, pudge, viper,...etc)
counters: to counter him you need magic resistance ( anti mage, rubbick) and some guys like terror or shadow demon who can make use of venomancers on their illusions, and items like pipe is a disaster for him.
scepter effect : Increases ulti damage and decreases cool down. Damage per Second: 60/85/110, Cool down: 140/120/60.
huge amount of DPS that can be really annoying to some heroes.
low mobility and not tanky at all
low damage and not very effective when silenced, specially if is not maxed.