We can confirm the icon then.
My test showed the Keeper Icon larger than normal Icons (And it does appear for me, he spawns in hell, so were you looking there?)
I posted it before the update that fixed it.
I tested the bosses again (in expert mode). For now, the Sea Serpent is the easiest of them (not a bad thing) The projectiles it shoots are brutal if hit, but you can survive a hit. The Serpent Eyes however, does only 1 damage with solar armor on.
Dark Skeletron is at least in expert mode, by far the hardest. The ray it shoots seems to do a good amount of damage I think, buth a hit from the head, and possibly the minions, and you lose at least over half of you health. It doesn't help that it's near to impossible to dodge his head. What I think will solve that problem, is to slow down Dark Skeletron, so it is possible to dodge him.
The keeper already has an icon but only on my game because I haven't released the update yet. Do you like his size or should I change it; I love your idea of being chased through hell by a giant mouth
While I could say that you can make him a bit bigger so its harder to go past him, it doesn't really matter. He's hard to get past now, and even if he was bigger, you could always just dig a tunnel over him. So the size can stay how it is now. The only way to prevent someone from getting past him, would be to give him the tounge effect that Wall of Flesh has.
Besides that, he is possibly the most balanced boss. He isextremely hard on expert mode. All his attacks do high damage, and he can really take us out fast. However, with enough planning and arena setup, I think he's beatable, just incredible hard.
Edit: do you like my new avatar, I made him myself.
Awsome! Much better then what I can make if I tried. Bill Cipher from Gravity Falls, and the leader of Illumonati (Just kidding

). I really enjoy that show, yet I haven't watched much of it, since I don't watch much tv these days.