Most monsters can be killed by death rays. There's no guarantee it will stick on the first casting though.
Death Ray and Petrification won't work on (m)any powerful monsters, but disablers such as stunning, blindness and paralyzation, which leaves monsters completely helpless, work on everyone.
Some monsters are immune to many of these effects, actually. Undead and constructs in particular are immune to most disablers.
Hoping to win with every class, doomed. Archer, Barbarian, Bard, Beastfighter, Druid, Elementalist, Farmer, Fighter, Monk, and ULE Priest down.