Tony Hawk SHRED

For this, you need 15 insane Challenges total.

I recommend completing all 7 Videographer challenges first, as they're by far the easiest.

Next easiest are the 5 Combo challenges, which require you to run the entire stage in a combo (Manuals to jumps to grinds etc). You have a few choices here:
1.) Be badass and complete them normally. Keep your balance manualing the entire level, jumping when needed.
2.) Place something around your board to hold on to, to keep your balance.
3.) Just use your hands and tilt the board. Keep the balance arrow for manuals in the middle range. Ollie when needed and place board back tilted before you land.

General Tips: Find best path with least airborne obstacles/grinds, least gaps, etc
Always remember to keep board in manual position when landing.
If you're good at Olling in manual, I suggest hitting long rails as you can't fall off them

Now, you should be at 12 total challenges. The remaining ones are actually hard. They take the form of the regular (easy, medium, hard) challenges, but usually have much much more difficult requirements. I found the Snowboarding ones to be a little bit easier to do, since they have less complicated moves, as well as the first few Skateboarding levels.

Do three and the achievement is yours.