OK, if you switch to Slayer form, you lose rep points. If you switch too often, your alignment switches to the evil equivalent (Chaotic, Lawful, or Neutral). If you switch when you face teh Sarevok Wraith, you will change alignment when you use that tear. If you use it during the FINAL battle, my understanding is that you will also switch. (I never tried that one, so I could be wrong. I have read it on this, and other forums)
Now.
Final battle.
Just before you use the last tear ---> TANK UP! cast every protection and enhancement spell you have (It's the final fight, what are you saving them for?). After using the tear, Jon comes in, and you get the cool dialouge(sp?)
"SWORD... MEET EVIL!" LOL
Pull the mages and clerics back (unless you've been using Jah as a tank). Jon brings in four buddies, demons. Prot from Undead, or Evil work here. Minsc, Keldorn and you should have no problem taking them out. Potions of extra Healing, and spells from the backups. While you fight the four, Jon will cast Misdirect, and you won't be able to target him until you take out the image of the Slayer. He does this aagain after you take out the first. Then it's you against the Slayer.
The Slayer starts out Immune to everything, but if you wait, spread out and move around til you hear the "dispell" sound, you'll be OK (That's why you need to take out the buddies first) Once the Immune from Everyhting is gone, Breach, Miscast, or Ruby to get his protective sphere down. Then pound oin the bad guy! Remember, the Slayer regenerates, fast. As much damage, as quickly as possibel is the only way.
I took him down with my good-aligned party twice. I used Vicky insteead of Jah, and Valy instead of Aerie, but the rest of the party was the saem. These strats worked for me, the second time.
The first time, I got Confused, and my main char ran around, being stupid. The rest of my party died, and when I came to , I finished the job. It's why I went solo. I replayed it, to keep the party intact.
Hop this helps, and let me know.
------------------
The RudeDawg
Known in these Forgotten Realms as Perin LightEyes
and my girlfriends, Pamila and Phil