Caroline's Kiln

This spell has not been thoroughly balanced. It was created as a concept. Use it at your own discretion. 

When you cast this spell, you create a cube up to 30ft on each side. The area you choose must be a cube before calculating area restrictions. The kiln spreads around corners but does not go through walls or areas that are completely sealed off (unless the sealed off area is entirely consumed by the area of the spell, such as a chest). The area begins to warm, dealing small amounts of damage at first, but increases in power the more times it afflicts enemies. The more power that the kiln has, the brighter it glows, going from transparent, to red, to blinding white. 

You may choose to extend the duration of the spell by expending a spell slot higher than 2nd as an action. For example, you would cast the spell at 2nd level, to extend it once you need to expend a 3rd level slot, to extend it again you need to expend a 4th level slot, and so on.

All creatures within the kiln are afflicted at the end of your turn, or when they move into it for the first time that round. The kiln only increases in power after all afflictions are calculated at the end of every turn. For example, if a creature gets afflicted outside of your turn, the kiln will increase in power at the end of their turn.

Any saves that the spell forces must be made at the start of all affected creatures' turn every turn if the creature is not already under the condition.