I agree that pre-placed invincible lemmings should be possible.
For now, I've decided not to go ahead with this. I'm not sure if it's possible to enforce "only allow 1 invincible lemming per level" code-side without introducing potential bugs. Note that the Editor would also need to support this as well. There would also need to be code to ensure that the lem isn't invincible
and a zombie/neutral, which also adds mess.
With that said, if you want to have a pre-placed invincible lem, simply place a regular lemming in exactly the same place as a single collectible, ensuring that the lemming is positioned over the collectible's trigger area. When the level starts, they will immediately grab the collectible and become invincible - this will also trigger the sound effect, letting the player know that something is different.
Yes, this means we can't have multiple collectibles
and "pre-placed" invincible lems in the same level, which I realise nerfs the collectibles feature somewhat if people end up wanting to use it just to make pre-placed invincible lems. I might reconsider this decision later if there's demand for it, and if this ends up being a regular use case.
this can be vital for enforcing solutions
With SuperLemmix, I'm aiming to encourage designers towards "multi-solution" levels. If a feature ends up
helping to enforce "single-solution" levels, I'll most likely want to remove or seriously revise it!