Alright, first thing, climb up that vine-covered wall while waggling your Tail Whip at him disarmingly! (If that doesn't work, then just climb the wall and forget your tail.) Use the height to cover yourself from Heph's attacks[/I], you should be able to duck behind that ledge so that his ranged Ice Beams and stuff won't reach you. Stick close to the waterfall while you're doing it, so any Yawning he does is drowned out. Chameleons are good at climbing, right? Yeah, I know there are lots of your kind near Fortree City, where you can't do anything if you CAN'T climb around. Now while you're up there, duck out of sight and Recover some health. Then Sharpen your Claws to get ready for the next round. Oh, and if he even thinks about making a Substitute, Snatch it away before he gets the chance.
climb up the wall while using Tail Whip (staying close to the waterfall to drown out sounds) > Recover > Claw Sharpen
SUB: Snatch if Heph tries to Substitute