Recently, I've finally beaten Lunatic Cultist and decided to fight Moon Lord. The first 2 times I died, because his lazer kept hitting me, since I can't avoid it. Now I found a way to defeat him. I put myself in a box while only the Phantasmal Spheres can damage me. But now I find myself pretty confused. On the site it said that only the Phantasmal Sphere attack can go through blocks, but it never said anything about his tongue. Now, I need to know this, so I actually can defeat him in a small time, because then I would need to concentrate on his tongue so he doesn't heal 5000 health every 40 seconds.
Now I really need to find out this, because it will be quite a long time until I'll get my Beetle Armor.
Did anyone used the box technique like I'm planning to use and knows the answer? (I'm going to use the Godly Solar Eruption and put the Nurse down, also that hole won't be there). 
Best Answer
As per the wiki, yes, the tongue/tentacle can reach through solid blocks. However, it's still a good idea to have some kind of platform above you in your arena, since the Phantasmal Deathray does a LOT of damage but can be blocked by solid blocks.
Additionally, the tentacle is technically dodgeable, though it's very difficult. If you manage to get beyond its range, it can't attach, but be careful because if you get too far away Moon Lord will just teleport to you.