Updated for 3.0
New Chaos Dwarf spells added. Spells updated with vanilla 3.0 values. Missile spells different miscast cooldown effect tweaked.

Dwarf petrification physical resistance tuned down to 20%.
20 second spell & abilities recharge delay tweaked.

Dwarf rune magic miscasts given tiered damage.

Miscast damage now tiers with the mana expenditure of the spell:

High 18+ mana spells: 32 HP damage per entity, 16 non-AP plus 16 AP.Mid 12-17 mana spells: 16 HP damage per entity, 8 non-AP plus 8 AP.Low 0-12 mana spells: 8 HP damage per entity, 4 non-AP plus 4 AP.

Because miscast damage tiering requires editing the spell tables directly it will be less compatible with other magic mods that also edit vanilla spells. For greater compatibility with such mods I've reuploaded the original edition of Miscast Mod here you can have the option of switching to:
https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=2937404714

Update for v2.1.
Malus of rune magic miscast contact effect adjusted to the new -35% magic resistance for dwarfs.

Tweak to dwarven petrification miscast contact effect. Adds rock hard 25% physical resistance and immunity to psychology, at the cost of losing their 25% magic resistance, slowing affected units by 80%, and a small fatigue malus, for 20 seconds.

UPDATE:
The Dwarf 'Locus of Power' passive ability from Anvil's of Doom will now cause enemy casters to have giant miscast explosions every time they cast a spell. Thanks to Yiunko for the suggestion. Have fun.

Update for Immortal Empires. Changed some of the vfx animations with new WH3 options, tweaked the Dwarf rune miscast. May further revise.