DOTA Nevermore guide
A powerful Defense of the Ancients hero, the Shadow Fiend is great for large amounts of burst damage. His skills allow him to release area of effect nukes. His ultimate is much more devastating, provided the dark lord hasn't died recently. It releases a cloud of souls imprisoned within him, slowing everything around and doing ridiculous amounts of damage. There's also a casting time though, giving people who can the chance to run away.
Laning phase
This is a starter guide about how to play Nevermore. It doesn't go into depth about all his skills and things for stats junkies. If you want an item build, try the Shadowfiend guide for ideas.
You don't have a lot of health, so be prepared to play carefully. I typically buy boots and a stack of gg branches. Use your shadowrazes to help prevent melee heroes from being able to last hit. You might not be able to kill them, but the mass AOE to their face should keep them from bugging the creeps too often. Use both the mid & long range ones to hit them twice. However, you should watch your mana! Level 1 shadowraze does not do much damage. Try to wait until at least level 3 as Nevermore before you use your nukes.
This phase is pretty easy as nevermore. Check the runes. An invisibility rune, coupled with your shadowfiend nukes, should guarantee you a first blood or at least a DOTA kill. You can help gank enemies early on, or you can sit in the lane until you've got your ultimate Requiem of Souls. The skills Nevermore has makes him extremely useful roaming for weak heroes.
Lategame
This stage is the worst for Nevermore. As a nuker, your strength lies in the early & middle game. However, your spells aren't all that useful anymore. You should still try to land them of course! The requiem has a slowing effect that is also very helpful, as well as the large burst of damage.
At this stage you might want to try going DPS Nevermore. The easiest way to do this is with skill synergy. Your presence of the dark lord, a skill most people think is worthless, amplifies physical damage to any enemies nearby. It's around a 20% damage boost. You can mix it with both a Stygian Desolator and Assault Cuirass for a whopping -16 to armor level. That should more than double the damage to anyone you and your allies are targetting!
This can work even better coupled with other heroes. Dazzle, with his weave, is an excellent companion. This lowers the armor level of enemies over time to completely demolish it. It's -30 (over a long fight) if Dazzle has an Aghanim Scepter! Nevermore also synergizes very well with Slardar the Slithereen Guard. His amplify damage will lower someone's armor by 15.
You can also try going with a support build. A caster Nevermore would be equipped with items like a Guinsoo and Shiva's Guard. These will help out greatly during team battles. Either way... you should try to win the game before it gets to this stage! Nevermore is very weak to high strength tank-type heroes, especially the dragon knight, centaur and lycanthrope.