Bounce

A bounce,<ref name=":0" /><ref name=":1" /> return to sender<ref name=":0" /> or rebound<ref>Maybe the line of thinking was that Kathryn and Ellie would fail in a

similar way to how Molly had.  Maybe, as she’d prepared other

individuals with knowledge of how to deal with demons, she’d anticipated

that they would destroy themselves, attacking Laird or Alister or someone and
having the demon rebuffed, sent back to the summoner.  A demon, ready

at hand, that was capable of bypassing the typical defenses. Leaving the impulsive, stubborn, aggressive Kathryn and Ellie ill prepared for the rebound. - excerpt from Sine Die 14.10 </ref> refers to the natural tendency for harmful magic to rebound on the sender if successfully rebuffed.

Summons and hexes which are sent after a target, but successfully rebuffed, will often "rebound" against the summoner stronger than before. They could then be rebuffed by the original summoner, sending them back against the original target - but if they are bounced back a third time, they will be significantly strengthened.<ref name=":1">Bogeyman came with a container, practitioner broke the container? Approaches to binding rituals.
Sent bogeyman to go murder someone in the most horrible ways possible, but they were blocked, and came back to me, what does the practitioner do? Do the same thing, and hope they aren’t equipped to bounce it back for the third total time, because it would be far stronger on the third trip. - excerpt from Malfeasance 11.2 </ref><ref name=":0">One of the bogeymen they’d sent out the door only a minute ago.
“It’s a bounce!” Alexis called out, springing to her feet. “They blocked her somehow! She’s after the nearest available target!”
Return to sender.
A very good reason many practitioners were very careful before they sent a curse or a demon stomping over to their enemies. If they fucked up, or if the enemy was clever or strong enough, that same curse or demon or whatever could come back, stronger.
[...]
“Bounce her back,” I said.
“Antique box,” Alexis said, standing just to my left. She held a box

a human might have been able to fit inside, but only if they really

contorted themselves. “Not sure how to get her in it, but once we do, we can push her outside the library and remove the lid.”
[...]
The box fell, cracking on the floor.
Each return-to-sender makes the summoning stronger, I thought.
- excerpt from Malfeasance 11.8 </ref><ref>Barriers will serve their purpose, but hexes and deleterious magics will often glance off the Bane, rendering them a potent devise against the unwary. Without expecting their workings to go awry and come back to them, such a Magus might find themselves dealing with their own practises and the Bane both. - excerpt from Duress 12.3</ref> This is because of the power, hostility and outrage they absorb from the person rebuffing them.<ref>He was wrong about what the crow was, but he still managed to capture and bind it.
He sent it back at the ones who had created it, with a touch of added power, hostility, outrage, given freely, and the compact of the Invader’s ways of dealing with spirits. A seal, which made the crow both less of what it had been and more a part of things. A different manner of things.
- Interlude 11 </ref>

If there's no original sender, or it can't be returned to the sender for some reason, the same effect can cause some rebuffed curses or Others to simply bounce back to the target after a while and attack more powerfully.<ref>I noticed the doom and followed it to her. She was fending it off, but

the way a curse, an omen, or a sending works, if you can’t bounce it

back at the sender, or if there’s no sender, it can magnify. The doom had swelled, going away for a time, picking up strength, then returning. - excerpt from Out on a Limb 3.4</ref>

References