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The item_antidote can be found in only one Half-Life map, the multiplayer map datacore. However, due to a glitch, it immediately falls out of the map. It can be retrieved using noclip by flying directly below the stairs in the room with the longjump module. The item_antidote was replaced with an item_battery in op4_datacore, which does not fall out of the map. The antidote is not found in Opposing Force, Blue Shift, or Decay.

The ammo_9mmbox, also referred to as chainammo, was not used in any Half-Life or Blue-Shift maps. The entity was used by Gearbox and can be found in Decay in ht07signal (x2), ht10focus, and ht12fubar (x2); and in the Opposing Force multiplayer maps op4_park, op4_repent, op4cp_park, op4ctf_chasm (x2), and cp4ctf_dam (x3)