The walkthrough below allow you to unlock all areas while earning Koins along the way. It's possible to earn around 80,000 Koins just by opening chests and unlocking new areas (Not including quick-time-events). There are QTE's (Quick-time-Events) that will randomly trigger while you're exploring. These are usually deadly creatures that will ambush you, and you have to press the displayed button to protect yourself. The quicker you press the button, the more Koins you receive (Usually around 500 Koins tops). Failing the QTE won't have any negative impact in your exploration except the lack of additional Koins.
Full-access and All-Koins Walkthrough
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1. The krypt has a tutorial area which provides 4,000 Koins and promptly requires you to spend most of them to continue. If you're starting with nothing, then head N to (0,9) and then E. A QTE will occur at (2,9) and even the smallest reward is enough to buy the first Koin unlock at (-1,11)N.
2. Buy the koins at (-2,7)W then circle around to (-5,21)N. You can buy more koins from the chest between 3:30 and 10:15.
3. Pick up Scorpion's Spear at (-13,19)N and Sub-Zero's Ice Ball at (-21,20)N.
4. Open the map and return to the Krypt entrance. Your next destination is the
Spider Tunnels at (3,9)E (backtracking would just take longer).
5. Buy the koins at (7,10)E and pick up Raiden's Staff at (5,11)N. Keep to the
right as you proceed N, E, and S.
6. Buy koins at (9,2)S and keep hugging the right wall. When you reach (18,4)N
you will use the spear to cross the gap. Get the Spider Gem at (18,10)N.
7. Turn around, use the spear again, and continue following the right walls.
You'll use Raiden's Staff at (20,19)N to pass another gap. Go W.
8. When you get to the Spider Gem Hold, head N. Get Reptile's Claw at (6,30)W.
Go E and at (9,30) go N to reach the Switch Passage. Go E first.
9. Pull the levers at (15,34)N (17,34)N (15,34)S and (17,34)S IN THAT ORDER.
10. Get Kotal's Sword at (22,34)E and buy Koins at (21,35)N.
11. On the far W side of the Switch Passage, use the sword at (6,35)N. You need Kenshi's Katana from (5,40)E. Now backtrack to the Spider Gem Hold.
12. Use the Spider Gem at (4,26)W. Between 7:00-9:30 use Raiden's staff at (6,24)S. Buy the koins at (5,21)S then teleport back.
13. Facing N, you can keep following the right walls to backtrack all the way to Shadow Spider Kave. This will also result in a u-turn to the next area. When you reach the Chamber of Bones, get Kung Lao's Hat at (-7,12)S.
14. Go W to find an incline going N. Follow it to (-10,21)E and use the hat. Exit the tunnels at (-11,12)S.
15. Buy the koins at (1,17)N between 11:00-1:55. Go W, open the gate, and go N
to use Kenshi's Katana at (-2,21)N.
16. We'll be heading clockwise in this tomb, so follow the left walls after you get Liu Kang's Fireball at (0,6)N. Buy koins at (-4,8)W as you continue.
17. Use the Ice Ball at (-8,14)W and pull the lever across the gap.
18. Get Ermac's Pendant at (-5,18)E and use Raiden's staff at (0,19)S between 7:00 and 1:15. This will take you to the Lost Mausoleum. Buy koins at (5,-1)E and use the staff at (0,0)W. Go N.
19. Use Reptile's Claw at (-5,28)N and pull the lever directly in front of you.
Continue following the left walls to the S and then E.
20. Use Ermac's Pendant at (9,14)E and pull the final lever at (13,14)E. Resume
clockwise travel and buy koins at (2,8)N.
21. Open the gate at (0,9)N and get Jax's Rocket Launcher in front of you. Buy
koins at (1,14)E.
22. Use the rocket launcher at (-11,12)N. The Kamidogu needed to access the
final map is obtained by gambling at the shrine here. Placing 10,000 Koins will ensure that you'll get the Kamidogu on the first attempt.
23. The Kamidogu is used at (-24,18)W but there's nothing to accomplish there
now. The final koins can be obtained by using Liu's Fireball at (-20,4)S and
buying (-21,1)W.