That is the regrettable part of the current state of the game. I WANT to build there but I won't until it joins the rest of the survival game. It sucks having to ignore an entire biome because it currently exists outside of the zombie survival game. If zombies couldn't enter the Plains biome and never spawned there and if in fact all I had to do was step five paces into the Plains biome and be perfectly completely 100% safe there I wouldn't build there either but wouldn't exactly call it not a big deal....
Hopefully someday the underworld biome will join the rest of the game.
UGH. Just so you know, I'm trying man. lol. I'm really trying. Below is my latest hair brained idea. But I started killing it off as I wrote it up.
* No matter what digging mechanic, you'll now have to widely defend, at a bare minimum, 5 sides of a cube. With no real great pathing bait like doors. That seems REALLY excessive. Suddenly you now have the equivalent of flying zombies. ALL zombies as flying zombies.
* You're also pitting a situation where you have 5 cop zombies land right up against your forge room wall or ceiling and no way to know they're coming really. And even if you knew they were coming, this becomes ridiculously complex to balance game play IMO.
Uh... How bout this?
Firstly, what I'd call the bigger challenges to getting zombies underground:
* Horizontal/diagonal digging causes SI issues. Indirectly causes excessive player maintenance potentially. Busy work = bad.
* Immersion as to how and why zombies got underground.
* Stupid little pitfalls breaking legs and killing people. We're all tired enough of broken legs. Right?
Uh... What about... A Horde Vertical Digging mechanic?
Random zombies, like those found around town don't really belong to a horde so this would not apply to them. Wandering, Screamer, Blood Moon hordes would be affected (maybe not screamers, might just become too much).
If horde targets player underground and no air path (air/doors/hatches/ladders/etc) to the player exists within say 50-100 blocks? Then Horde Digging mechanic kicks in.
Horde kinda groups up together into a tight pack. All zombies hunker down and start digging. Hitting all blocks in a 3Wx3Lx1D range. But ONLY vertically dig above the nearest air pocket that connects to a players foot block. Have the zombies hits act like explosions. Causing debris to fly around (existing mechanics). Giving surface indicators that "zombies dug a pit here".
Now... Pause. lol.
You get the following results (probably not seeing this from all angels).
1. Zombies work their way down below. Underground becomes part of game play.
2. Happens enough times, there's going to be a few vertical shafts around your base that zombies will navigate too before going into Dig Mode. I.E. get as close to a player as possible, identify player foot location once and cache that as the ongoing navigation target point. So eventually, yeah, you'll have pits. But zombies will stop digging them? maybe?
3. None of the digging is horizontal.
4. Some surface indicators of a pit plus a larger pit is easier to spot. Less annoying broken ankle/falling in random little hole instances. Though yeah, you're gonna die more from these types of pits than diagonal ones... >.>
Still... Can get pretty swiss cheese. But at least without affecting SI because all shafts are vertical.
This problem is really annoying me... lol
The whole damn thing takes me back to Cavern POI's. Like you say Roland. "It's a Biome". So let's use it like one.