Essentially, the same spell would "oxygenate" an area. As a ritual though, you're casting it ahead of time... hard to do if he's about to cast fire and you want to cause it to blow up in his face. Easy to do if you know he's a fire-guy and place it early.
I like the aspect on the scene (instead of yourself) because the free tag can be transferred *at your discretion* to someone else in the party, if need be.
Other ideas:
Hedge Maze (as thaumaturgy)
complexity: varies, usually 7-9, plus extra for size or duration; fairy tale castles may exceed 30 or more!
The caster first outlines an area with grains and fruits, flowers, or seeds of common shrubs or bushes. Once enclosed, the caster places a few more lines completely across the area, making random intersections, and then closes the spell. The caster can draw an "inner circle" of an area to remain clear and surrounded, if desired. If a building is to be surrounded, then all of the zones adjacent to the building must be included in the complexity. If the building is to be covered inside the maze, then all of the zones that the building contains must also be included. The shrubs and bushes then grow to great height, forming a hedge maze around the area. The maze does not necessarily follow the pattern drawn by the maze, but the caster must specify two openings (either two on the outside or one outside, and one on the inner circle), and whether or not the maze is open at the top or if the hedges form true tunnels. The caster instantly knows the way through the maze, as well as anyone that meets a condition set by the caster according to the rules for ward recognition.
All other people must surpass a barrier strength equal to the complexity of the spell, minus any shifts spent on size or duration, to pass through the maze. To overcome the barrier, a person can use might (to break through a section), weapons (to hack through) or academics (to solve the puzzle) for each zone that they pass through. For high complexity mazes, this could be treated as accumulated successes... however, the maze shifts and regrows any damage every few minutes, making such a trip a one-time deal.
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