Fear-Based Magic (5e Variant Rule)
From D&D Wiki
Normally, when you want to use magic again, you must rest first. With this variant rule, resting does nothing for your magic, instead, you must cause fear or other negative emotion in those around you to regain it. Any character that can use arcane magic starts with 30 magic points and may cast magic using this pool by spending one magic per spell level. You may not cast magic at a higher level than you would normally. When you deal damage, or if the dm decides you can, you may make an intimidation check contested by every creature that can see you's insight. you may also make this check with disadvantage in exchange for those who can hear must also participate in the contested check. Any creatures who fail their insight check is frightened and you gain 1 magic. any creature who rolls a one on their insight check fails automatically and you gain 4 magic.