I've been playing on Hardcore with ease, and I've narrowed down the reasons why it is easy:
As long as you travel at day, you never encounter mobs; animals are abundant; there is no long-ranged mob.
1. You can sleep pretty much anytime, especially in a treehouse, and the mobs die. There are two options to fix this: Either make it so you have to kill any mob that has seen you during that day and is within a certain radius, maybe 10-20 blocks (edited post here), or only half of the mobs (not including the creepers) burn at day.
2. There are too many animals when you spawn. I've heard that animals only spawn once, when chunks are generated, and they spawn extra to compensate. I believe this, too, because my server has no animals now that we've killed them. Anyway, I spawned next to a big crowd of cows and pigs and killed enough for more than a full armor set and enough food to last me pretty much forever once cooked (and even when raw). I think less animals should spawn per chunk, but they should...um...create more animals by themselves so they keep their population going. Maybe they can only make more if a lot are killed (you know, because of food supply, they can't become too populated).
3. Skeletons need way more range and line of sight. I mean, they traded attack power and rate for range, and their range is pathetic. They should have about 3x the range they have now so they can be a real sniper mob but still have less range than the player. Of course, their accuracy wouldn't be as good from that far away. Maybe they can move closer while shooting.
number 2 and 3 are valid points but you cannot sleep if there are mobs to close, this feature was added in 1.9 pre release 2 i believe.
I know, but it's a very small radius and is very glitchy. It always lets me sleep when skeletons are looking at me through the window, and once, it didn't let me sleep because there was a chicken nearby!
Actually, I'm changing my mind about the first one. Editing the OP. The real problem, I realized, is that you can run from mobs and sleep to get rid of them. If you stay in your house and want to sleep, you shouldn't have to kill mobs who have never seen you before.
As long as you travel at day, you never encounter mobs; animals are abundant; there is no long-ranged mob.
1. You can sleep pretty much anytime, especially in a treehouse, and the mobs die. There are two options to fix this: Either make it so you have to kill any mob that has seen you during that day and is within a certain radius, maybe 10-20 blocks (edited post here), or only half of the mobs (not including the creepers) burn at day.
2. There are too many animals when you spawn. I've heard that animals only spawn once, when chunks are generated, and they spawn extra to compensate. I believe this, too, because my server has no animals now that we've killed them. Anyway, I spawned next to a big crowd of cows and pigs and killed enough for more than a full armor set and enough food to last me pretty much forever once cooked (and even when raw). I think less animals should spawn per chunk, but they should...um...create more animals by themselves so they keep their population going. Maybe they can only make more if a lot are killed (you know, because of food supply, they can't become too populated).
3. Skeletons need way more range and line of sight. I mean, they traded attack power and rate for range, and their range is pathetic. They should have about 3x the range they have now so they can be a real sniper mob but still have less range than the player. Of course, their accuracy wouldn't be as good from that far away. Maybe they can move closer while shooting.
And I thought I'd link this too for more ideas, Sting_Auer's thread: http://www.minecraftforum.net/topic/869838-making-minecraft-more-challenging
And this, my critical damage suggestion (heal slowly when injured a lot): http://www.minecraftforum.net/topic/868876-critical-damage/
Support shields replacing parrying here! (Click it)
I know, but it's a very small radius and is very glitchy. It always lets me sleep when skeletons are looking at me through the window, and once, it didn't let me sleep because there was a chicken nearby!
Support shields replacing parrying here! (Click it)
Support shields replacing parrying here! (Click it)