A380 Wake Turbulence
From my own experience as a B777 pilot:
have twice now flown into the descending wake of an A380 (visually identified) in the cruise, with us being opposite direction below, 1000' vertical separation (RVSM). Both these experiences led to quite an exciting ride for 15-20 seconds, with up to 30 degrees roll left and right. Memo to self - in RVSM with opposite direction 380s above, a 1nm offset right routinely might not be a bad idea...........