There are two Doom Hunter Base Toy Locations for you to find.
All Toy Locations in Doom Hunter Base
Lost Souls Toy
The Lost Souls toy is found in the smelting room of the base. Once you've cleared out the demons, head to the back of the room where a platform is moving up and down.
Jump onto it, and turn around. You'll be able to see the secret toy in a circular vent ahead of you. Double jump as you move forward, and time your double dash ability to make it into the vent.
Hell Knight Toy
The Hell Knight Toy is found near to the end of the level. Before you head into your final major fight of Doom Hunter Base, you'll walk down some stairs and into a room full of ammo and health.
Before you do, turn around and look up. You'll see one of those green targets that you've been able to shoot throughout Doom Eternal so far. Shoot it, and the staircare behind you will make way to a secret area. The toy is in here.