Hello, since I have completed all of the quests, I decided to make a walktrough. I am not going to make it very long, so enjoy This is my suggestion on what upgrades to make at first: The most important ones you need for the beginning are: Armor, speed and ammunition. Upgrades like Gliding and Luck will be useful in later level, and Prospect is good to have in the beginning depending if you want to get money faster, but upgrade it after the first three suggested. We have left with Piercing, Dodge and Dexterity..they will be the last ones to upgrade. Also, the most important move is Stab or Up Slash.
And now for the quests/medals:
Tackling Pro
Kill 15 enemies while sliding. = For this one, just go to one of the first levels and slide against the weaker monsters using ''z''. You might need to repeat a level 2-3 times to complete it, but it's not hard.
Harlequin Style
Use the Harlequin costume and parachute, Cane and Apple. = For this one, you have to pass about 2-3 levels perfectly. Go to the shop, buy the second armor (with the hoodie), fifth weapon (fishing rod), second projectile (apple) and second parachute (the colorful one) and then complete a random level with it.
Pacifist
Complete level 1 without killing any enemy. = For this one, go to level 1. If the monster i over an object (for example a rock) and you are over it as well, press down to dodge him, another way is just skip them by jumping. Basically stay away from them and avoid them using jumping, or going under them if they are over an object.
Perfectionist
Complete 5 levels at 100% = For this one pass the first 5 levels, they are the easiest. The reach 100% of the level: rescue 3 civilians of each level, complete the challenges as well and you shouldn't get hit. Do those tasks on the first 5 levels and there you go.
Bird Hater
Make all birds fly away in level 5 (don't miss one). = For level 5, don't be afraid to get hit. The idea is to be close to the birds, so they can fly away. You just need to get rid off all of the birds by jumping next to them.
Ranged Rampage
Kill 6 enemies using projectiles with Infinite Projectile activated. = For this one, it is good to have the luck upgrade, because it will increase the chances to find a flower. I would suggest level 5, because even though it doesn't have a lot of enemies, it is easy to get a flower and it is easier for the quest/medal. The chance to get Infinite Projectile is 25%, if you don't get a flower after reaching 50% of the level or don't find the Infinite Projectile, just restart the level until you get the flower, go to the lady and get the Infinite Projectile to kill the 6 enemies.
Quick Death
Kill Black Captain (on level 4) in less than 20 seconds. = For this one use fast mode (go to options to find it) and once you reach him, the tactic I suggest you is: skip the cutscene, after his first atack before he uses his sword again jump on him and then jump to dodge his other attack. Repeat it quickly, but always atack after his first atack, so you don't lose time.
Sword Master
Perform a combo x50. = For this one, go to level 9, not 10. Because in level 10 you can get hit easily and the range between enemies can be long at times. For level 9, just atack all of the enemies without being hit and keep in mind the duration of the combo. Buy the Cursed Gauntlet from Black market to have an extra second of combo duration. Be sure to hit all of the enemies you see, use projectiles when needed, it will be easier. And again, be careful because you might get hit and the combo will reset again. You will need a few tries until you get used to it
Epic Hunt
Get 15,000 points or more in the Infinite Hunter challenge. = For this one, I suggest you to have all of the upgrades, and finish the other challenges as well to have more Soulons, so you can buy the upgrades. Make a pattern for each phase you go through, on the more difficult ones for you, use projectiles. My personal idea is, since you have 3 lives. On every 5000 points, you need to lose a max of 1 life. If you lose 2 lives before reaching 10000 points, restart because it will be difficult for you. And again, make a pattern or way to go through every phase, to make it easier for you. You have to fight exactly 200 monsters to reach it, this needs great experience and patience, so good luck.
Final Rush
Complete level 10 with fast mode ON. = Turn fast mode on (go to options). On level 10, don't concetrate on passing the first part of the level, just go to the boss by not attacking
the monsters and dodge most of the atacks, don't be afraid of being hit, on the boss battle you will have full armor. For the boss battle: to avoid the fire flames which increase by one after each time you hit him: move a little bit to the left if a flame is coming next to you, or you can jump/skip it, it's not hard to dodge them, but be careful. Also move around the teritory if you want, this way you can have more variety and basically just make sure you are far from him, so when he tries to attack you, the fireballs will be spread. For the electric balls: DON'T stand under him, I have done this mistake many times, move away from him and double jump to skip the ball. For the blast: once you see the mushroom jump over it and press down, so you can jump even higher and use the parachute to stay in the air. Once the blast finishes, just hit him. For the raining fireballs, mind how and where they are falling. Go to the left end, and go a bit on the right and watch carefully how they fall, then move away from the one that is over you if it is reaching you. After you are done with the first phase, he will shoot you with fire balls one after another and on every 5 of them you will see a blue orb, which once you take it will atack him. To dodge them just follow this: down ball - normal jump. Middle ball - slide, or jump. Top ball - double jump, or don't jump at all.
I hope this helped you, have a great play and thank you for reading!