Ok the first number if accompanied with (x levels) means the unit levels up at that mark, note when i say vets, I mean, gets as fast as possible on that level. Units seem to vet with fewer kills on higher levels (not difficulty levels).
Mancers - 150-180 kills or so (3 levels) - vets around 90-110
Pathfinder - 150 ish kills (4 levels) - vets around 110
Mortar - 220 ish kills (4 levels) - vets around 140
Strider/Demo - 130-150 kills (2 levels) - vets around 100-110 (demo bugged)
Archers - vet around 90-110 kills (they are not to be mocked)
Ranger - not too sure, think it vets a bit quicker than archers. (grab roots so you can heal pally if he gets stoned)
Mazzarin - without either aura, he vets at 30 or so kills. he needs far more kills to melee fast with defense on and less with haste
Paladin - vet around 40-60 kills (THIS IS YOUR MOST IMPORTANT UNIT!)
Forest Giant - 180-200(?) kills (4 levels) - vets around 110
Berserk - uhh...40-60 kills? (2 levels) - vets at like 20 kills and again at 70 ish
Heron - 30-40 kills (then most of them will become heroes (low mana heals)) - vets around 25
Squires - Yeah right..... well ok - they seems to vet around 30 or so, but they are useless units that should only really be healed with mana or heal bursts
As to the Demon Lord, just run away as soon as you see it. I don't know the exact length of time, but it respawns every 30 mins or so. I have NEVER seen it killed or anyone get close to killing it.
If you really are determined to try and kill it I suggest this...
Multiple Iron Golems + paladin regeneration on DL + holy clouds + lvl 3 electro storms + lots of basic para bows to keep DL paralysed.
Heck, even that might not be enough, it really isn't worth trying.
![Shocked :shock:](./images/smilies/icon_eek.gif)