The other solutions are great. I did the "20-???" portal scrolls and banged it out pretty quickly. Here are some tips for the grind:
- If you are reading this before starting the game, play on easy. I played on medium and, at that difficulty, the grinding levels will be full of these wizard things that can kill you pretty quickly (see below). You can't switch difficulty after starting the game :(
- While playing the game, pick a weapon class and stick with it. This allows you to dogpile all your ability points into one ability, maximizing your damage. You might need to put a few points into the other abilities in order to use some armor or weapons, but it won't be much (20-30 points, maybe). As far as I can tell, they are only used for combat with particular weapon types and don't affect anything else (e.g. strength doesn't affect how much you can carry, etc.).
- As mentioned in the other solutions, you want to have Adventurer maxed. Use a potion of respec if you need to reassign your points. Have a friend gift you one and it'll be free.
- Whether you are using the special dungeon or 20-??? portal scrolls, ignore as many of the grunts as you can manage and hunt down the larger, fame-giving monsters. You can drastically cut down on the time it takes to grind out the achievement doing this. I also ignored most treasure pickups unless they were close.
- Make haste one of your spells. You can cover ground much more quickly that way and run past a lot of the mobs when looking for the fame monsters. This is useful for the main game as well.
- Give your pet a summon spell as one of its spells. The creatures it brings in make nice distractions for the mobs while you hammer on the fame monsters. Your pet will use it fairly often.
- Try to keep your pet from fleeing by using the "heal all" spell when its health gets low. Pets are pretty much worthless in combat but make convenient distractions. The heal all spell is almost identical to the heal self spell except for a trivial increase in mana cost.
- Your main weapon should restore health on hits. It's best if this is a natural enchantment of the weapon (either when you bought/acquired it or via the enchanter). You can use a gem in a socket for this but it takes a loooong time to get even a decent gem and it will be nowhere near as much health as an enchantment.
- Gems are a waste of time. Just sell them. If you get an item with sockets, buy whatever the gem seller has to fill them. You can get much better results from the enchanter (just remember to quit to dash if you get hosed).
- The better/worse arrows in the inventory are not reliable when you have a lot of enchantments on a piece of equipment. I think they just consider DPS and armor value. Be careful of that when replacing things. Also, you will never complete an equipment set, so don't even bother trying.
- Be careful of the wizard things that summon little skeleton guys at high levels (I forget the name - "dark" something or other). They summon little fast-moving little skeleton guys and cast powerful spells. One at a time they are not that bad but they can be deadly in groups.
- The little energy ball things can also be unexpectedly deadly in large groups. Their attacks make the screen really busy so it's hard to tell when you are getting mobbed.
- Clear out the mobs around a fame monster before tackling it, especially spawners like the gravedigger. If you don't do this, you can get unexpectedly mobbed and it's frustrating to have to run back to where you died.
- Make sure you keep an eye on your health. The game is crazy easy on medium difficulty except for when you get mobbed by tons of baddies and when this happens, you can die surprisingly quickly. When things get hairy, pop off a push-back spell or haste to a safe spot to heal up. Also, don't be afraid to use health potions when you need them since there a lot of them throughout the game.
- If you are doing the bonus dungeon, make sure to complete both quests from the guys by the door, or three if you managed to finish the ember guy quests so you can do them in the bonus dungeon. Before going down the staircase at the end of a level, use a town portal to return to town and complete the quests. When you get new ones, they will be for the next level (which you are about to start).