Bearing in mind Alch is the fastest farming hero in the game, it probably comes as no surprise that as core Alch your sole focus should be on getting as much farm as possible. Acid Spray is your key skill in the lane: it deals damage to your opponent, which makes it easier to get last hits without getting constantly harassed. Later on, when you have more levels in it, it will push out the wave pretty fast. You can use this free time to stack the nearby jungle camps. In the later laning stage you can farm them with Acid Spray and your ultimate for sustain.
MAJOR:
Fastest farmer in the game: Alchemist is by far the fastest farming hero in the game. While heroes like Anti-Mage, Medusa, Luna could reach 900-1000 GPM with a godlike game, Alchemist can achieve that without really breaking a sweat.
Can stack and farm fast in the jungle: Acid Spray can be used to stack from far away, to stack 2 camps at once or to stack ancients from the low ground.
Tanky in the mid game: The ultimate combined with a decent gold lead allows him to be pretty much untouchable if not focused by multiple heroes.
MINOR:
Versatile builds: There’s more than one way to build him, allowing you to become a farming machine, tanky Radiance carrier or a physical damage carry. You can farm enemy camps with Radiance/Manta illusions, split push and fight with an early Radiance or different items.
Can boost his teammates with Aghanim Scepters: This could be a huge factor for supports who have good upgrades like AA, Witch Doctor, Rubick or carries and offlaners who need different items but have good upgrades.
Juicy bounty runes give him x2.5 gold
Fun and unique hero