Hardmode

If you have not tried it already... Hardmode is, well, hard. Unfair, might be a better description. Keeping the word unfair in mind while you play Hardmode would do you some good. There is not much to say about Hardmode, but I'll do my best to inform you about the differences I have noticed.
 * Monsters have increased HP and ATK. They are able to spot you from greater distances, making the rogue's amulet less useful.
 * OH! And some monsters move faster. There is no running from fast spiders. Plan your moves accordingly.
 * Monsters spawn in randomly more often. Close doors behind you every now and then if you don't want them coming from behind you.
 * Use greater caution when testing spells and potions until you have identified the more dangerous ones (toxic, flame, earths fury.... but there are also stun and freezing potions). On the first two floors, you are likely to pick up at least two of the three, and their effects seem to last longer.
 * From game to game, certain groups of items seem to spawn less while others spawn a little more. You may find yourself with many potions only one or two scrolls.
 * Basically, the RNG makes things go a little less in your favor. If you find a LUCK amulet, treasure it.
 * Bosses are slightly different. The ogre, for example, now has a reach of 2 squares.

==================================================== == Tips and Advice

In Hardmode you have to take the precautions of normal mode and step them up a notch.
 * Be aware that when you choose a class you can take runes from other classes in the adventurer section. For example, a warrior could take a mages energy absorption rune. This allows you to choose more useful runes from classes, though you can take only from each class (including your own class section, you can theoretically choose two from your own class).
 * Before making the decision to spend one of your precious ankhs to revive, seriously think about how your run has been going. If you are deep down, but are constantly struggling with food, health, or broken weapons, it may not be worth it. You likely won't make it. On the other hand, if you died simply because you stood in water fighting an electric mage or fell into the piranha pool... maybe go for it.
 * You may not be able to hoard your weapon upgrades as you might have in normal mode. Having a weapon that can 1-2 shot the monsters is worth it. If you have the materials, you can simply transfer the +3 or whatever to your new shiny weapon. (Before upgrading your new weapon!!!) This is discussed more on the weapons page.