Before entering Hell, stock up on red potions and the magic scroll that damages all enemies on screen. Don't use anything before fighting the Devil, then go all out with magic which counts like a drill hit on him. I think he needs 8 hits to die. Use a potion when you're at 25%.
If you didn't get the Medium achievement, exit Kong and then complete the level where you earned the last coins to 43/43 again. At least it worked for me.
I think you need 1000 Happiness in order to get 5 Stars because I got the achievement with 1109 and 4 Stars with 905. If you score a guy with an annual multiplier of 25 very early on, stick with him until the end. I never found the perfect (looking) guy before 40.
If you complain about Lv 25 being too "hard", you don't deserve the Medium badge. Get a frigging grip, it's a platformer with puzzle elements. I don't see anyone complaining about the SHIFT series featuring hard jump 'n run sections either.
Found 3 endings so far *SPOILERS* Good: Don't collect all the gems (there are 11 but you only need 10). Instead, climb up, open the chest near the start and return to the temple. Not so good: Same as Good but kill at least 10 creatures with lightning. Bad: Collect 10 gems, return to the temple and use the light to go up. There's a creature in one of the caves that will teach you the Teleport Spell after killing 10 other creatures with lightning.
Does the creator of this game actually knows how long it takes to collect 20 damn shells?
And does he know that in every other RPG monsters drop potions?