In creative mode you can spawn a zombie with the egg
First go to lith harbor and click on the black taxi which brings u to dungeon. then go all the way right and u should find a hidden teleporter go all the way up till you can't go anymore then press up and u should be in there.
Yes, in the Nether Zombie Pigmen spawn on the netherrack but I don't think they spawn on Netherrack in the Overworld.
blockland fourms
travel up the tree that grew 3 then head towards the portals
The game has a preset spawn pattern which will only keep a certain amounts of monsters onscreen at a time. If there are very little monsters onscreen, there must be a platform somewhere on the map that is FULL of them. Find it and kill them and you'll reset the spawn.
it's a random spawn chance, I believe it is possible by using spawn eggs which can be obtained through the creative inventory.
I assume it's a quest item drop from annoyed zombie mushrooms at the map "Singing mushroom forest: Ghost mushroom forest"
Mushmom, Zombie Mushmom, Lycanthrope, Wolf Spider, Dual Birk, Spirit Viking.
You can get it from Zombie Lupins, Jr. Lupins, Ice Sentinel, or from the King Bloctopus.
No. Unless it's a glitch, the only way you can spawn them other then mods or console is going into the NPCs section and manually spawning a zombie.
No, mushmoms do not need a special item to be summoned. They have a specific spawn time which is 45-60 minutes.