I'd make defiling class options. If you're a sorcerer, wizard or warlock, defiler is your origin, school or pact. Selecting another origin, school or pact would require a DC 15 Will Save (addictive defiling is hard to resist...).
You'd always attempt to defile when casting a spell if you are a defiler. When you attempt to defile, you'd create a ring 5' in diameter per level of the spell. All creatures within must make a Con check (your spell DC) or they lose the ability to do reactions until the start of your next turn, additionally, all inanimate plant life and small (insect) life in the radius is reduced to ash (fluff mechanic - monster foes are not impaired). If there is no plant life or small life (and no creatures fail a save), you do not defile. When you defile, your spells are cast as if you used a spell slot one level higher (for example, a 1st level spell cast using a first level slot is adjudicated as if a 2nd level slot were used).
Once you get to 6th level in those classes you gain one (additional if you are already a sorcerer) metamagic option from the sorcerer class. You do not gain any (additional) sorcery points when you gain this mechanic. However, you can use your reaction to harvest a bonus sorcery point every time you cast a spell of third level or above and there is plant or animal life within the radius of your defiling aura (DM determination - remembering that each casting will destroy all such life in the aura). You may use these bonus sorcery points as normal sorcery points would be used to power your metamagic option(s). When you use a sorcery point, increase the radius of your defiling aura by 5' per point spent. You lose all bonus sorcery points if you have not gained one in the last minute. You can have a maximum of three bonus sorcery points (if you would gain one but are already at the maximum, you do not reset the clock for keeping these bonus sorcery points).
At 10th level, you gain the Chill Touch cantrip, or another cantrip from your class if you already have this cantrip. Gain 1 bonus sorcery point if you deal damage with Chill Touch. Your limit on bonus sorcery points rises to 4, and you do not lose your bonus sorcery points unless ten minutes expire without you gaining one. You also gain a second (additional if you are a sorcerer) metamagic option. You may replace the metamagic option you selected at 6th level with a different metamagic option.
At 14th level, if a creature dies due to damage inflicted by your spells (including cantrips) or dies within 10' of you, you gain 1 bonus sorcery point (or 2 if they died due to Chill Touch). You also gain 1d10 temporary hp per creature killed by your spells or killed within 10' of you. Normal temporary hp rules apply. You may replace the metamagic options you selected at 6th and 10th level with different metamagic options.
If you're an arcane trickster or an eldritch knight, you gain the base mechanic defiler mechanic (but not the 6th, 10th or 14th level augments) unless you make the wisdom save and select to be a preserver.