Your potent Necromancy grants you the following benefits.
Critical Failures
When a creature rolls a 1 on the d20 for a saving throw against one of your spells, it suffers a Critical Failure. It fails the save regardless of its modifiers or the spell save DC. If the spell deals damage, you roll all of the spell's damage dice twice and add them together, then add any relevant modifiers. This additional damage applies only to the creature that rolled a 1.
Improved Critical
Your spell attacks can score a Critical Hit on a roll of 19 or 20 on the d20.