Fast Death Knight into fiends is one of the most standard and safe builds that undead has. It allows the undead to quickly tech to tier 2 and tier 3 where undead unlocks some of its power spikes (like statues and getting orb at tier 3).
Difficulty of build: Not as basic as fast fiends but still an easier opening for newer players.
Pros
- Fastest possible hero.
- Early access to fiends.
- Quick access to tier 2 and tier 3 allowing for a strong mid game and access to timing attacks.
- One nerubian tower can hold off most harassment along with your units.
Cons
- Lack of map control at the start of the game as fiends slowly build, however, strong middle and end game.
Race Match Ups
- vs Undead: Effective against all openers but requires adaptations depending on enemies strategy.
- vs Orc: Very fragile early on but most optimal at Tier 2 and Tier 3.
- vs Human: Good vs all strategies. Effective at early game harassment, requires strong tier 3 timings.
- vs Night Elf: Good vs KOTG/Warden and weak vs DH.
The below graphic indicates the basic build order up until tier 3. The video goes more in depth on how to execute the strategy.