Purpose: to inform players how to unlock the ultimate racer for the purpose of attempting world records.
This guide's purpose is not to run through each course and state how to complete them. That just takes practice. :)
The Iceman / Crystal Boarder: You will need to beat this guy on Expert Match Race to unlock him. Completing Expert Match Race is also the only way to unlock Deadly Fall¤. After the credits roll and the game returns control to you, go to the Select Rider lodge. Zoom in on Akari and tap C-left. Then confirm Akari as your rider. Selecting secrets in this game is unlike Cruis'n USA. Holding the button down seems to work only part of the time. If you see a blue ice portrait on the Board Select, you're set.
The Panda / Rob Haywood looking like an idiot After you've unlocked Deadly Fall, you can go into every stage in Time Attack, Trick Attack, and Contest and beat the top three scores. As long as EAD no longer shows as one of the records, you're in the clear (although nothing is stopping you from calling your own records EAD). After you've cleared out those records, go to Rider Select, zoom in on Rob Haywood, and tap C-right on Rob Haywood. Confirm Rob as your rider. A panda head should appear on the Board Select. EDIT 7/19/19: You only need to beat the 1st Place record in Time Attack and Trick Attack. Time Attack records can also be beaten in Match Race mode, as long as you wait until after the credits/ceremony screens to enter your initials. In Contest Mode you can time out as long as your score beats the 1st place score (still have to do this three times).
The Penguin Board (Warning: if you unlock this before you challenge the Gold Boarder, he WILL use it to race you) With the Panda unlocked, you can go to Training and complete the Trick List. [EDIT 10 SEP 2018: You do not need the panda tricks to unlock the penguin!] There is a bug that allows you to do a hard trick by doing an easy trick: select a simple trick, perform it, double-tap c-right in mid-air, select a hard trick, tap c-right to close the list, and land. You will need to use a few characters to complete the trick list. After completing the trick list, go to Board Select, hover over any board, and tap C-down. Then select the board and your stance. This should start you off on the penguin when you enter a course.
The Gold Boarder / Golden Ice Man / Lagger of Courses with trees in them You must beat Expert Match Race with the Ice Man. Once you have down this, it's C-Up on Kensuke, same process as described above. Note: if you save a ghost of the Gold Boarder, he will not be transparent. This could be annoying, but you can press C-right during a course to toggle the ghost.
The c-up/down/left/right explanations are so complicated because tapping is far more accurate than holding the button, and most cheat/faq/walkthrough sites say to hold it and hope for the best.
Once you've unlocked the Penguin Board and Gold Boarder, you've unlocked the ultimate speedrun machine. The Iceman is good for edging, and the Panda is good for jumping off the sides of courses and messing up 1080s and 900s with front flips. The Gold Boarder really does seem to lag Golden Forest, especially with a ghost present, mostly because the game has to calculate all the reflections¤.
¤not verified
I hope this helped. I may Tweak (300 Points) this in the future, but I think it's fine for now.¤ -arcticfox
Changelog: 10 September 2018 - corrected information on unlocking penguin board (thanks to someone I forgot in Discord). Changed a typo. 19 July 2019 - corrected information on unlocking Panda Boarder (thanks to route improvements in 100%).