Oh, I didn't realize the ranger was in the demo version.
If so you can unlock the druid by playing a ranger/healer, and the druid is a really awesome magic job.

As to job combinations, as I said, it is likely that the reason your not doing damage if your combining magic and technique based jobs is that your characters development is all around weaker, a fighter/thief will be developing their physical stats twice as much as a fighter/mage, and so far worse at attacks.

This might also explain why your running out of mana to cast spells, since the amount of mana you get each level depends upon your intelligence, and once again, a mage/healer or a necro/mage will be getting twice as much intelligence as a fighter/mage, not to mention that with lower intelligence their spells will be doing consequently less damage.

As I said for a very easy combination, try a necro healer, or if you have the ranger and can unlock it, a necro druid.

For a technique based job, try a fighter/thief, since assassin is not available in the demo version.

Hth.

@Chris, the unlock combination for the druid is ranger and healer together, and for the adventurer as thief and wanderer.
Adventurer's are pretty dam useless owing to locate secrets being really not much good without pick locks, and even with pick locks unlikely to find you something helpful, but druids are absolutely awesome!

Druid necro is a really great combination particularly because lightning is a great offensive spell that hits multiple targets, and it's one drawback, that if it hits a corpse it creates a zombie is easily negated by playing a necro and using a targeted banish undead (or for that matter a targeted iceblast), on the zombie's head.

I've finished the game with a necro druid in the party several times, indeed probably the easiest time i ever had was when playing an  elf necro druid, a gnome healer necro and a half elf necro druid (I got very lucky with my rescued companions that time).
The ratkin race is intended as a major challenge with their morphing into giant rats. The only miner problem i had is that like the shaman's phase form ability, there was a really annoying bug that when polymorphing between different creatures all of a character's stats got set back to racial defaults.
this was fixed in the latest beta, the one that required weerd components, but not in the last stable main version, which is a shame since it makes ratkin a real pest to play.

the 2.0 alpha is actually entombed Ii I believe and is a very short concept demo.

the 1.5 test is I think the version that Jason tried rejigging the architecture, but also fixed several bugs, so while it was largely less stable and didn't run on most machines it did have that fix for the stat restore with shamans and ratkin, I probably ought to test it myself since I do need to reinstall the game on this computer.

Generally you are best off with the 1.02K  release as it is the most stable and the only really major bug is the problem with ratkin and shaman, which were the last two things added to the game in 2010, indeed you can play shaman quite successfully so long as you don't use their phase form ability.

Btw,  to upgrade to 1.02K use the update patch from the entombed update site, Download it here indeed that version might even have the ratkin fix in it's been a long time since I read the release notes).

Well jason added to the game constantly for three years, then in 2010, with a new job and two new children he had to put development aside.
Combine this with the fact that the game code, due to so much being added aparently grew quite eclectic and it's likely entombed is pretty complete, though the game is certainly far from being an early version and highly playable, it's just that extra functions such as scripting to create custom content or fundamental changes in the game's system weren't possible with the existing code.

Whether Jason will do a final bugfix I don't know, but in the mean time we still have an awesome game either way, even if one that didn't get all the planned expantions.

More recently (as of last year in fact), Jason returned to development and started work on Entombed ii. There were some very very veeeeery! early alphas which experimented with things like a ranking system and a different style of exploration which would more easily make for things like environmental hazards and avoidable fights, and development was promising, but where things are now I'm not sure, still I have a lot of faith in Jason and am sure we've not heard the last of things, though more likely with entombed Ii at this point.

Even with original entombed, back in 2007 the initial alpha was nothing to write home about, then around a year later boom! suddenly a major game with huge amounts of content hove out of the blue.

Entombed is based very much of the principles of a roguelike rather than a final fantasy style set rpg. So, rather than having specific characters and a story, you take a single character down into a dungeon with lots and lots of combat and randomness. Indeed one thing i really like in Entombed is that a lot of the tachtics involve thinking on your feet and deciding what your going to do with what resources, characters and situations the game throws at you rather than maximizing your options with equipment and over all tactics with a specific set of stuff.

Hope you like the game, any questions, please ask.

glad your liking entombed, and I can highly recommend the full version, just from the job and racial choice alone it offers so much more replay aside from the fact that it has another 17 dungeon floors to go down.