ToME: the Tales of Maj'Eyal

Play Stone Warden.

Enter Ruined Dungeon.

Activate Meditation. This triggers Earth's Eyes passive ability.

Dig out tunnels to each of boss' room.

Dig out one diagonal hole to the room, with Stone Vines active.

Summon your halves.

Retreat.

Rinse and repeat.

Is it, like, cheating?

Naa, it's just a good(if tedious) strategy. It won't work on every dungeon.

Earth's Eyes enable you to reveal a 12-step radius.

I play in ASCII mode. If there's a monster in a location, ToME won't display a dot -- instead it shows a blank space so you KNOW there is something though you don't know what. The viable strategy is to dig out a parallel corridor, as close as possible, turn on Meditation et voila.

Helped a lot in Dreadfell.