Legendary ring in Legion, AKA the Execute ring. It makes the execute free even during the last 20%, unlike SD which only makes the basecost free. This means that if it procs in the execute phase and you have SD up, you'll waste it on a 10rage execute, rather than a full 40 rage one. I haven't seen anyone who has the ring, so not sure if you can cancelaura the buff, but it's still a real annoying ring to work around.