Another video. This one during the final two turns will actually show the differential in damage rolls with, and without Jigglypuff in play...
Battle Vid#: 36-03894-79440
This will show Pory-Z hitting Swampert two turns in a row with Tri-Attack. The first time Jigglypuff is on the field, and the second time it isn't.
My Swampert is flawless IVd, 252/0/0 Defences with a neutral SpDef nature.
The quality of my opponent in the first battle is a lot better, but the second video shows compairable damage.