Some times I like to throw a little twist in there. Something in those odd times when success is actually failure and failure is actually success.
I know this sounds weird. The concept actually spawned in my brain a long time ago with Castles & Crusades. The C&C Illusionist is the coolest one I’ve seen. I haven’t kept up with additional printings, so I don’t know if there’s been any changes in the class. But in my old version, Illusionists got healing spells but there’s a catch. For them to work, the target has to FAIL as Save vs Magic.
Don’t use this idea too often or the weirdness wears off. Every time a character makes some sort check or Saving, they are assuming that the best outcome will be if they succeed on the roll.
This can be applied to the triggering of magical trap or item. Reading ancient runes or scripts. Or even crazy interaction with NPC’s.
Like I said, this isn’t something to be used too often. If everything is weird and topsy turvey then, nothing is. Just another little trick for a DM to keep in their back pocket if things get a little boring.
They Might Be Gazebos! 
The C&C Illusionist is indeed truly unique! One change that was made in the new 8th printing of the PHB is that it is now the Illusionist that has to make the saving throw to successfully heal the target (the challenge level is the HD/level of the target).
The reasoning is as follows. If you read the chapter on how C&C Illusionist magic works, you read that Illusionists are imposing their will on reality, “they do not trick the target’s mind into psychically healing itself; that assumes the target is mentally able to do such a thing. The power of the illusionist does not reside in the target; the illusionist’s power resides solely in the illusionist” (p.111 PHB 8th printing; p.72 in the 7th printing).
C&C makes it clear that, unlike AD&D where people could “disbelieve” an illusion, this does not reflect how Illusionists work in C&C. Previous printings have always had this inconsistency in the spell chapter descriptions and the contradictory healing spell descriptions. Having the illusionist make the save finally reflects a unified presentation of how illusionist magic works.
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Recently I was in a party that was running low on food during an overland journey, and we did everything we could to increase our chance of wilderness encounters, in the hopes of encountering something we could eat. It worked, and we feasted on roast gator all the way to our destination.
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