Venomancer is a mid hero designed to ruin someone's day. With frequent harrassment using poison sting, your enemy's regen is toast. Gale can be used to both setup ganks for your team and ruin an enemies gank with its 50% slow while your plague wards can be used for scouting as well as taking down towers. Stay behind your team later on and siege the enemy base, but also chase down enemy heroes when they try and flee the Venomancer; they won't be able to.