Quick Mastery Level 20 for unlocking the Marktplace

First of all press 'N' and claim your "Blocky Bonus", it's a free mount from the shop and Trion will probably add new mounts every month, so you can already get your first 50 mastery and amount so you are a bit faster.

Now you should focus on getting the starting character, for that just do the tutorial quest and always go to the highest world as soon as you reach the PR required. You can progress through the first words pretty fast until you reach a PR of 160 and that is already the point where you can stop leveling.

Always farm some shape stone while you progress through the worlds so now you can increase your ringcrafting to level 50 to get a pretty high boost on mastery. Just craft 50 rings and you are fine. After that you can deconstruct them to get back some of that flux, but keep at least one of them.

The next step is that you go back to the first world and get 1 hat and 1 mask from there that a level 1 character can wear. Go to a forge and upgrade them both to 5 stars and then press 'J' to change your character and then select the first character in the list and click on trial. Now you can play as this character for free, but he can only level up to level 4. So now upgrade his weapon to 1 star and go through all other characters and do the same.

The next step would be to go to the second world, the Permafrost World, and select one of the other characters, now equip the 5 star mask and the 5 star hat and one ring on this trial class and you can level him up to level 4 with just 2-3 dungeons and without changing the world since with all the upgraded stuff plus the 1 star standardweapon he should be at 60 per. Now just level every single character to level 4.

After that you should be at least at 19 Mastery if you also collected and deconstructed every single item you got from all this leveling.

Now you already could be at 20 Mastery, but if not you can try to also level gardening to level 50. For that just get some sunlight bulbs in the peaceful hills bio to craft a gardening bench or go to some random cornerstone in the hub world and just use the bench for someone else.
Another way of getting the last bit of mastery would be to use the starter class coin you get from the shop and level another class some more levels, since it's faster thanleveling your first class.

You also can use a Refer-A-Friend code from another player or your main account to get a free starter class coin so you can unlock 1 more class to level it a bit. If you need a Refer-A-Friend code, you can use mine if you want, but you can only use ONE single code per account. Its "TCLNXLZMMN9KJ3QGMGD2".

After all this your unlocked characters arent really high leveled, but its way faster this way then leveling your main to level 15 or so.

If you have done all this you will be at mastery 20 without problems.