Can pre-hardmode bosses spawn in hardmode?

Question

I just killed the wall of flesh and entered hardmode in my world.

As far as I know, all of the Hardmode bosses can now spawn randomly every night - but only Hardmode bosses. However, the Eye of Cthulu spawned three nights after I killed the wall of flesh.

Can Pre-Hardmode bosses spawn too, after the Wall of Flesh has been defeated?

Answer 1

I presume that the Eye of Cthulu had not "naturally" spawned in your world yet?

If so, yes, of course it can still spawn after you enter hard mode, as long as the requirements are fulfilled. The requirements are, from the Terraria Wiki:

• At least one player in the world has at least 200+ health.
• There are at least four NPCs in the world. Note that the Old Man counts as one of these.
• The Eye of Cthulhu has not already been defeated in the world.

Answer 2

Yes, they may. Most the time you must spawn them like using they suspicious eye, clothier doll, slime crown and worm food, plus many more

Answer 3

Every single spawnable boss can be spawned and killed during hardmode.

They can not spawn naturally if they have been killed once ; this is to make it feel like you are the champion of the land.

However, during a blood moon the regular merchant will ask "Have you seen clula...scthu... The big eye thingy?", even if you have deafeted him. This leads me to believe he might have confused the Eye of cthulu with The Twins although this is very unlikely.