I mention the Pain Elemental mainly because there's nothing else in Doom it is really comparable to.
For the record, the Idea Base field is when your monster is specifically based on something, not when it's similar to something else. For example, if I made a monster specifically based on the Magos from Warhammer 40k
, I would put that in the Idea Base, but if I made something that was similar to something else in idea, but wasn't intended to be, I wouldn't put that in there.
Connection is for when this monster also uses actors, sprites or sounds from another (in this case, it's not a connection because it has its own
sprites, it's not using literally the same sprites from Heretic and Hexen). It's. For example, the Hades Elemental is connected to the Hades Sphere because it spawns Hades Spheres, but the Squire wouldn't be connected to the Baron of Hell.