That dragon priest... [SPOILER]
Don't worry about that critter. As long as the PC's anticipate something "undeadish" lurking inside--and they should, it's predictable--they should be able to deal with it...
My players' PCs already were 2nd level (after having subued Calcryx, and fragged oodles of Twig blights and rats and half of population of the upper level goblins), when after much bashing, grunting and hacking to get the coffin lid off, they were alert for surprises. The players were a bit nervous--that was cool. So, in our case it was Arngart the Half-Orc Barbarian, Borlo the Halfling Rogue/Sorcerer, Dannik the Human Ranger (NPC), Erky (module NPC), Falowayn the Human Cleric of Pelor, and Lars the Wiz-Conjurer. They had no magic items. Some had some oil though. Anyways, the party had essentially flanked the coffin two times over when the Trollish Dragon Priest "awoke" and pushed the lid off. Well, within 2 rounds the barbarian (incredible damage), the rogue (nasty x-bow user) and the conjurer (burning hands) brought the critter down to negative hps. Then they all quickly grabbed the monster and dropped it into the pit trap and set it alight. They used the secret passage to escape the smoking carnage.
With good strategy and effort resourceful players will easily overcome this encounter.
Dealing with Belak at the end is another matter! His entangle spells can decimate the party in the briars if you run him correctly. Even then peculiar circumstances can alter combat outcomes dramatically!... In our case the party survived only because of the rogue/sorcerer's cunning use of spider climb spell, and the barbarian's "luck"!
Borlo's x-box shots raining down from the shadowy cave ceiling spoiled many enemy spells... Meanwhile two PC's (the 2 clerics Falowayn and Erky) were so trapped by entangle spells in the briars they could only watch the "final conflict" and call out warnings! The fact that the 1/2-orc barb was so powerful (the player lucked out on 19 STR and 16 for both DEX and CON during generation) meant NOTHING would stand in his way! (Nothing ever did in the entire module--what a beast!) He over came the 1st entangle spell and moved in too fast out of the briar patch for a subsequent spell. (You had to be there.) Thus Arngart confronted Sir Bradford, and immediately used his great axe to do the "talking". Well, while he toasted the ex-pally in less than two rounds Borlo's bolts skewered Sharwyn. Ouch!
It was downhill for Belak from there...

Ah well, the players had fun and that's what counts the most for me too!

I played the 2 NPC allies in a realistic tactical manner, yet not take anything away from the players' glory. If there are NPC's in your players' party, they can become a deciding factor... Be careful.
All this to say the PC's better have their heads up at the end. It can go wildly to any outcome. Inspite of my planning and good attempt to run the module opponents logically, my players lucked out on circumstances and the initial caprice of PC generation more than anything else. I really didn't want to tweak the module to match the players' PC choices. I thought it should stand alone come what may. There's verisimilitude in that for me as DM--part of my fun. We all learnt things about 3E and we mostly enjoyed the adventure
