totallydeadaccountdude
Terrarian
Problem 1: Clarity of Summoning Conditions
Let's make an example. You're a new player. You've just been decked out in Ironclad gear and weapons, and are ready to fight the Eye of Cthulhu, but when you try and summon him... nothing happens, because it's daytime. This isn't apparent at first, but you need to summon them at night. This was a problem I struggled with when I first started, I didn't know what to do, because it wasn't apparent that I had to summon that boss under certain conditions.
Solution to Problem 1: Tooltip Tells the Player When To Summon
I'll take the Eye of Cthulhu example I just posted as an example.
Summoning Item
Summons the Eye of Cthulhu
Only consumable at nighttime.
This would help newer players out in a way that isn't intrusive in the game. Rather than being up in your face, it's a simple thing in the item's description that tells the players far more information than right now. This could also apply to stuff like the Worm Bait or Bloody Spine, them saying something like "Only consumable in the Crimson/Corruption".
Problem 2: Varying Punishment For Failures
Let's make another example. For some reason, you manage to fail at killing the Eye of Cthulhu in time. What does he do? He flies away. He goes "Oh crap, it's the pigs! Let's blow this popsicle stand!".
Now, what happens if you fail to kill Skeletron in time?
He rearranges your face by going mach 12 in your general direction.
Now, here's the problem with this.
A game should give a consistent punishment for failure. Whether it be the lack of satisfaction of NOT killing said enemy, or watching them turn your character into cherry jello. I personally have NO problem with the whole "Boss killing you if you fail" situation, but I just want it to be consistent.
I'm sure it's incredibly frustrating to have the Eye of Cthulhu fly away when you fail to kill it, but if you fail to kill Skeletron, you're punished with death. The Twins don't do this, the Destroyer don't do this, but Skeletron Prime, Plantera, and Duke Fishron do this. It's inconsistent.
Solution to Problem 2: Consistent Punishment
If you fail to kill the enemy in time, the outcome should ALWAYS be one or the other. Either the boss should flee, or you should be killed. This can also apply to enemies like the Eater of Worlds, Wall of Flesh, Golem, and Brain of Cthulhu, too.
Conclusion
Now, I understand this can be a bit nit-picky, but it's so inconsistent I can see newer players struggling with this. Summoning bosses is very inconsistent, conditions wise. And the punishment for failing to kill a boss is too inconsistent. It feels unfair that you get a seemingly random punishment for failure. It should be a consistent thing.