Storm Crow has 300% hit (can't be dodged 100%) and reduces target's hit rate by 100% (multiplicative) for 10 seconds on hit. Boss is only killable with characters that are capable of kiting at significant range, with the "never miss" suit set, or with perma-stun. Either change his debuff to a linear reduction, greatly reduce the debuff, or set the debuff on a timer twice as long as the duration.
Fog (rune/ability) reduces target's hit rate by 70% (multiplicative). Some characters in dungeons also have a dodge buff. The combination makes it so many characters can not hit these dodge characters (need about 190 hit rate for about a 5-10% chance to hit which requires the 40% hit buff and every equipment hit buff). Either change the debuff to a linear reduction or greatly reduce the debuff.
Thunderworm is basically impossible for any build besides healing missile to kill (because healing missile doesn't count as a hit). He's significantly harder than the level 400 and 500 bosses. With 5 hits, Thunderworm hits maximum AOE and becomes permanently immune. For Blood Blast builds, your charge hits draw his AOE and he's immune by the time the explosion occurs. Keep the AOE, get rid of his chain lightning, and get rid of any damage reduction.
Damage Return (rune) in dungeons is only completable by builds that either do burn damage or builds that can one shot the mobs. Remove this rune or greatly reduce its effect.