Not Updated For Current Season
The masteries shown here are not yet updated for the current season, the guide author needs to set up the new masteries. As such, they will be different than the masteries you see in-game.
First guide ever, will add stuff + layout some other time.
This is the build I've played for several months now. The 0-9-21 masteries are something I really love, you can spam your mushrooms (<3) in early midgame and also harass with blind + poisened attack in early game.
Try to get solo mid and go there as fast as possible. Run into the middle and get invis there. Then be patient until you see all 5 enemies on map (4 if one of the is in jungle). Leave invis with normal shot + blind on enemy hero or just stay defensive. You can also get a teammate with ignite and let him fight at middle while you stay invisible. Let them both damage each other. Wait for the right moment and kill him with blind + ignite and maybe even a flash for a final crit ;).
The early [W]s make your very fast, later with berserkers greaves in midgame you're alot faster then anybody else. This also goes for lvl 2 since most likely nobody else has boots then.
Get mana/cd buff from time to time and use it to spam mushrooms. With a mined mid, flash and early [W] your almost ungankable.
If there are invisble enemy heros, get a ward (except for twitch, you can solo him with fast blind + ignite).