And I have just beat expert Skeletron. Finally, damn. My first try, some time ago, was space armor + space gun. Bastard trapped me inside his head, death followed swiftly. So for the past few days I gave it a try again. Put down some fireplaces around dungeon entrance and extended the upper part with platform. First try was with amazon, because despite claiming space gun is totes enough for pre-hardmode in the past, I've realized I was a foolish, foolish man. However, it didn't go so well. I've realized I have some problems hitting his hands, the way he flails around with them. Tried some different combinations, including harpoon and crimson bow and then space gun again (all that on top of all the possible buffs I could come up with). Got him to drop one of his hands with the later, while using a minecart, but died again due to poor planning. So I tried with recently acquired Medusa's head... and it was quite good! Got him to drop both hands, but the fight was dragging off for too long, and just before the clock turned 4:30, he hit me with his head, killing me.
At that point I've realized my main problem was not actually seeing the bastard. I had shine and night vision potions, but they just weren't cutting it. So I put some high dirt walls around and torches on them, lightning the whole area. Tried again, combined Medusa + amazon and that was it. With some planning, surprisingly easy once you get rid of his hands, actually. No cray-cray mode like low-life EoC. Also found mechanic immediately. I guess that means it's finally time to start with my space yacht project though, I've been expanding my underground temporary NPC shelter for far too long.