The end battles from this run are a little more involved because of the lower levels of the characters. Before even entering the final castle I placed the U-ray attachment to talon since it will be his best offensive circuit during the final battle.
I kept the standard party consisting of two humans and two mutants. In this play through I managed to not leave a character dead or incapacitated after a battle. The proof of this is found by looking at everyone's experience points. Everyone has the same level of 36, current experience, and remaining experience points with the exception of Sharon who has 14 less because she does not join the party until after the first simulator battle of at the beginning of the game.
After showing the status, equipment and such I begin the process on step below Balor in Xagor's tower. From here I engage Balor as the first battle.
After the fight Balor tells you about Xagor's revival while he is on his death throes. I head up one floor, grabbing the nuke for completeness, and continue up through the floors along the linear path to the final boss. I stop a step away from the final encounter, don't get directly in front of him or you will usher the final battle, to get my bearing and replenish magic for my characters. By the time I get to the final boss I am at level 37.
The final battle consists of a combination of Xagor and Sol which include different tactics since my levels are still a little low. The battle begins with Sol trying to hold Xagor at bay from possessing his body. During this time you have plenty of time to prepare for the true battle with Xagor and score some hits against the final boss. I use this time to up my status so Xagor won't annihilate me at my current level. I have each character, equipped with fast cast it on each other to increase their attack power and have Borgin cast wall on my party members to increase their defense. From here you can pretty much just keep spamming these spells, occasionally switching Borgin's target to another member so everyone gets a wall spell. After a while towards the transformation I use Borgin's turn to give everyone elixirs to replenish the lost magic from the buffing rounds before Xagor appears and while they are still casting away to buff their attack. Sol tends to forecast when this will happen by his dialogue between rounds.
When Xagor appears he gives you one free turn before he starts attacking. While Xagor is putting up his barrier in round one I have everyone attack as the first. Afterwards things get a little crazy. You will note the damage is equalized where the barrier would normally cut it in half because of the fast spell attack buffing from the Sol rounds. In some cases the characters hit harder because of the extra boost and the occasional critical attack. The general form of this battle strategy is derived from the Ballor fight. Unless something nasty happens I have Matt attack with xcalibr, Curtis continuously cast "cure B", Gloria attacks, Sharon attacks, and Borgin casts "cure A". The strategy changes to have Gloria heal if Xagor is laying down consistent strong spells across the party and Matt is always good to cast "life B" if someone falls. He will spam "dk force" which has the tendency to instantly kill a party member. I always keep Curtis and Borgin healing during the whole fight if possible with Matt and Sharon handle the extra scenario revival of characters. During the fight Talon joins the fight with the u-ray I gave him beforehand which adds a little extra damage at the end of each round. As you duke it out eventually Xagor will open his mouths. When you see this happen you will know that he is about to die and the end of the battle is nigh.
After Xagor falls I let the ending play through along with the credits.