These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Demonic Spiders: Poison Mages. These guys fire out homing poison balls that poison your character and drain around 25 health (you start with 50). But that's only on the easiest difficulty — on harder modes, they drain even more! Although poison cannot kill your character, it'll make you easy picking for the other Mooks.
Hell, any mage enemy is this on Demigod difficulty. All of them are able to cast Magic Shield, which allows them to take a lot of damage (even more if it's orange), making them one of the most durable enemies (without the shield, they go down very quickly). And then they rapid fire their deadly spells at you, some of which are unavoidable (lightning) or homing (ice, poison), if not just plain damaging (fire)...
Game Breaker: A maxed out Flame Lash, along with level 11 Battle Mage (which makes your mana consumption zero), level 11 Siege Mage (multiplies your damage fourfold), level 9 Faster Caster (increases casting rate and mana consumption rate by 90%), and a +150% faster casting ring. You'll be doing over 12000 damage a second, destroying the shielded mages mentioned above and even bosses in less than a second.