The skeletons never used to be such a problem, well they rarely missed which was annoying... But now they're sneaky and pack more of a punch I believe, making them a lot more lethal with their ranged attacks..
Ghasts. >( They're a pain to kill and you can't really come outside of your base and do stuff when they're around.
And the sounds they make are creepy.
Endermen are annoying too, I made a watchtower where I stay at night to kill hostile mobs with arrows, the normal mobs don't even see me. Endermen teleport behind me and kill me (or take random blocks out of my watchtower ><).
Nothing I just make full iron armor and they do almost nothing, even creepers.... Before the last updates even with armor creepers could do something, but now? Nope they just destroy the blocks around you its pathetic...
EDIT: Been awhile since I played Minecraft, but its weird with full iron armor everythings a pushover. Apart from the Nether I guess, but havn't dwelled in that too much....
But hearing that hissing sound and getting almost no damage (I play on easy ofc, but its better than playing on peaceful, but still iron armor lasts so much longer than what it used to, and makes you almost invulnerable with the amount of iron I get).
EDIT2: Reason Nether seemed harder was because my portal spawned on a ledge high up, and those stupid thingies that fire crud at you blew a hole where I was standing and I fell into lava lol.. But I guess if that didn't happen, it didn't do much damage, but not sure coz I was thinking Argh Im falling, splat.