I struggled with this, as it's not linked to the standard Y + B attack like most Capcom DLC achievements!!
Cyclone Lariat is pressing
If you've played Street Fighter, you will recognise the standing lariat move (spinning in circles with fists - the one to cheaply complete all difficulties!).
Finish 20 enemies with this (you may need to weaken them first) and achievement is yours!
This can be any enemies, doesn't need to be humans.
"Mech-Zangief" is the initial unlock character, this skin / version is fine for this achievement!