At the beginning of this scenario, Grove summons the Death Lord, and then summons the rest of the enemies just after the fight has actually begun. It's worth placing tough characters on the higher pathways to the sides of the main floor, and you'll certainly need at least one tough Holy group going through the middle - the Death Lord and his Shades will absolutely annihilate anything else that tries to get through.

The Death Lord is the first major enemy in this scenario, and killing him is vital to its success. If you kill all the Killer Tiger, Golem and Werebear groups, Grove will simply summon more, but only whilst the Death Lord is still around. So, if you have people lagging behind in experience, you may also want to put them on the sides. The Death Lord charges down the middle so take care of at least one of the two less tough groups there (Incubus or Golem). As soon as possible, destroy the Death Lord.

After that, the battle is pretty much plain sailing. Archers to take out the Succubi and Wraith groups would be handy. Note that Grove's Witches are archers, and they're pretty good - weakening them with Spells, or charging them is the way to do it. However, his Dark Guard are very tough as well, so if you charge, make sure you have enough movement to get out of the way afterwards.