Anub'arak - Beetle Build

Take Beetle build if you're not playing for long range engages with Underking and just want to be a stat stick

Level 4

Bed of Barbs is a reasonable default pick. Never use this for waveclear or poke.

Shed Exoskeleton is reasonable if you want in fight mobility to keep up or juke.

Level 10

Cocoon unless they have good Cocoon break.

Locust Swarm if they have good Cocoon break.

Level 20

Rewind is usually the best option for strong late game impact.

Hive Master is a valid option for drawn out fights if you picked Locust Swarm .

The Traitor King can be picked if you're getting repeatedly bursted in fights and you're playing into a front-to-back comp.