Avatar leveling is pretty simple, and I think it makes a bit more sense now.
Instead of getting levels 1-50 of your next class's spells/skills/weapons at 101, the next 50 at 102, etc, you gradually work at them. For example:
You level up until you hit 99 and hit negative experience to level (Next Level: -123456789). You quest or somehow obtain level 100 and you're a Hero/Heroine. As a cleric, your first multiclass is druid, so you would get druid skills for 1-25 through levels 100 through 124. You would then go into negative experience again and quest for 125, which is Lesser Lord/Lordess and get skills for levels 26-50.
1-99 : Mortal
100-124: Hero/Heroine
125-149: Lesser Lord/Lordess
150-174: Lord/Lordess
175-199: Greater Lord/Lordess
200-224: Lesser Avatar
225-249: Avatar
250-274: Greater Avatar
275+ : Demigod/Demigoddess
You don't receive skills/spells/weapons from your multiclass for any level over 50. So if you're a cleric, you multiclass into druid first... you only get druid skills up to level 50 (so no blade barrier, stoneskin, etc.)
Now, to get from level 100-124, you have to be roleplaying to actually level. You can gain experience while not roleplaying (just like regular leveling) but to actually level you have to be roleplaying. You can get to negative experience to level again, and the first experience point you receive while roleplaying, you will level. By getting to "max negs" (just watch your Next Level number. When it gets to an even number and won't go higher, you've hit max negs) and THEN roleplaying for your level, you can actually obtain two levels at once.
Of course roleplaying in this sense isn't meant to be a means to an end, but that's just the way it goes with the new system.
Also, if anyone else who's returning after a long break from DL (read: before the recent pwipe), the areas are not where you're used to them being. Also, the level requirements for some items (as well as some of the effects) has been changed to better balance everything.
Sorry for the long ramble, and hope this helps you and anyone else reading
--Vulsin