Calm down... Calm down...
I've played through NQII around 3 times already, here are some tips:
~ Rohane and Talinia are good attackers so use them for their damage! Rohane can hit a max 100 with Father's sword and Tally can hit pretty well too.
~ Mipsy's damage spells are generally useless against him. They either get resisted or don't hit well. Use her to throw damage/slow potions at him or you can use haste potions as well.
~ I've noticed that haste potions work really well!
A hasted 65% Talinia and managed about 2 turns before King Terask's next turn.
~ And always keep him slowed. 80% slowed. If you run out of 80% slowing potions, just use 70% ones then.
~ Velm should keep the group healthy. If Velm falls, 90% of the time the rest of the party would fall as well. Also, Velm's shields should be kept up as well. Otherwise, King Terask can easily nail any party member down with 2 direct hits.(He can hit 200 damage on Mipsy if shields are down, beware)
~ Speaking about shields, King Terask II has his own annoying protection of Infinity as well. But here's a good way how to counter it.
When his shields are down, have everyone throw slow potions at him until he is slowed. Then everyone start lobbing damage potions at him. When his shields are up, Rohane and Talinia should start attacking with Meelee while Mipsy continues hurling damage potions at him.
~ If King Terask hits too hard, use the health potions instead Of Velm. Remember, you have more than 100 of them!
~ Lastly, if he uses Renew, don't feel discouraged. You can still win! Anyway, he doesn't spam Renew like Hubrid Nox does
~ Good luck!!!