The blueprint for the Crowbar is located in a secret area behind a special lore room where a scientist's corpse with a headcrab resides, along with that of the HEV Outfit. The room will always spawn unless both are collected and turned in to the collector.
The Emergency Door can be used to guarantee critical hits with the Crowbar even when there are no doors available, such as in boss biomes. Since the skill has a 10s cooldown, without any cooldown Mutations it leaves a 2 seconds window where the Crowbar won't deal critical hits before a new door can be deployed.
Along with the HEV Outfit, the Crowbar is a reference to the Half-Life series as the iconic melee weapon used by the protagonist Gordon Freeman.
Before v1.8, this weapon was teased in the game as an easter egg in the background of Weapon Mercheants.