Clear the two Lightning Skeleton Arenas in the Great Temple, either solo playing as Jaguar, or co-op playing as any characters.
If you have a cleared game save on Hard, load that up and head to one of the stone faces. Warp to the Great Temple, and head to the two locations on the map where the arenas take place.
Even though arenas don't respawn, the devs have re-triggered these two with the update so that you don't have to run all the way back through the game again, provided you never deleted your Hard mode clear file. However, you only get ONE shot at the achievement, so if you clear either of the two arenas by yourself without using the Jaguar character, you WILL have to go back through the game on hard.
Make sure to get your Intenso meter filled up, then trigger the first fight. As soon as the four-armed ground pounder enemy spawns, immediately activate Intenso and take him out ASAP. The faster you kill him, the fewer lightning skeletons you have to deal with.
For the second arena, again make sure your Intenso meter is full before starting. Clear the first few enemies. As soon as the hammer enemies spawn, activate Intenso and try to knock one of them down into the corner on the bottom level, opposite any remaining enemies from the first wave, so that it is besinde the hammer enemy that spawns in that corner. Fight these two in the corner away from the other enemies. Take out any remaining enemies from the first wave, then try to take out one of the remaining two hammer ones before the lightning skeletons spawn. Once they spawn, fight the two of them in the corner furthest from the final hammer enemy. After they're dead, finish off the 4th hammer enemy and nab your achievement.
For a visual guide, check the video below.