Hi, My name is Blinks, and this is how you play Shadowfiend Shadowfiend is an agility based ranged carry. His Q, W, and E abilities are ranged aoe nukes. His first passive, grants him bonus damage for killing units and heroes. His second passive reduces the armor of nearby enemies, and his Ultimate is a huge AOE attack with a 1-second channeled cast time. Last hits are more important for shadowfiend than to most heroes, as they not only grant him gold, but bonus damage as well. This mechanic can give shadowfiend a huge advantage early-game, but can also be a liability, as you lose half your stored damage upon death. This can result in you not have high damage output if you die a lot early game.
Shadowfiend will dominate teamfights if he is left alone. Since he doesn’t have any innate escape mechanisms, a shadowblade is needed to let you play aggressively. It can be a great tool for initiating if you can sneak into up to your enemies and get off an ultimate. Try to be in the center of teamfights to fully utilize your armor-reducing aura and devastating ultimate, but don’t forget that you still need to survive to do damage. When leveling Shadowfiend, put one point into Necromastery, and then max your Q and Necromastery before you get your ultimate. At Level 9, grab your ultimate and then prioritize it > presence of the dark lord > stats.
As far as items go, A shadowblade will give you a nice escape mechanism, and a bkb will ensure that you are always able to get your ultimate off. Late-game options include butterfly, manta-style, deadalus, or a heart for survivability.