Ok, so i was on smp4 at the central waistelands in one of those already dug mines, until i hear "you sense an eeri presence" so I walk out of my little mine to see what it was and quickly Ran out. Never going back there.
Sounds like you ran into marliax (or however you spell it) XD you should try and kill it because sometimes they drop rare items! EDIT: Marliax (Or however it's spelled) is a flying skeleton that shoots arrows and does a bunch of other cool, but dangerous, things. I think it spawns enraged skeletons (really strong skeletons) not quite sure though. But it does drop cool items.
The central wastelands outpost in one of the mines i think he east one. And would i be able to kill it tommrow with full iron?
Diamond would be preferable, but I believe it's possible with just iron. Maybe get some potions and bring those along also. And a strong bow.
No no, you'll need far better than iron. I suggest going out with some friends, get some regen potions and insta heals II, Not a guarantee you will all survive but atleast the marlix wont have as big of a chance living