There are 48 Medals to Obtain in in Zwei 2, You will recieve 1 of 4 Medals per-stage or Boss Fight.
Keeping the Scoreboard active will help on the conditions.

The Bronze Medal is awarded on minimum completion, Awards 7 Points.

The Silver Medal is awarded on completed with 1/3 conditions met, 8 points.

The Gold Medal is awarded at 2/3 conditions, 9 points.

The Platinum Medal is awarded at 3/3 Conditions, 10 Points.

For Ace Hunter, you will need 450 Points total, but the Highest Rank at 480 points is achievable.

As stated before, You will need to to complete a Stage or Boss on 3 Conditions to Earn a respected Medal, Conditions as Followed.

Stages

• Time
  
• Break (This applies to Pots)
  
• Damage

Bosses

• Time
  
• Food
  
• Damage

If Any Condition is Red, It mean you have Failed, If the Condition is Blue you have succeded, Although Time and Damage will be Neutral, it will immediately become red once over.

• 0 Points
  Hunter
  Reward: Bomb
  
  
  
• 30 Points
  Chaser
  Reward: Sliced Ham
  
  
  
• 60 Points
  Hunter
  Reward: Autonomous Charm
  
  
  
• 90 Points
  Hunter
  Reward: Fried Rice
  
  
  
• 120 Points
  Hunter
  Reward: Gourmet Chopsticks
  
  
  
• 150 Points
  Hunter
  Reward: Curry Rice
  
  
  
• 180 Points
  Hunter
  Reward: Virtuous Charm
  
  
  
• 210 Points
  Hunter
  Reward: Grilled Eel
  
  
  
• 240 Points
  Hunter
  Reward: Designer Purse
  
  
  
• 270 Points
  Ruin Explorer
  Reward: Turkey
  
  
  
• 300 Points
  Hunter
  Reward: Triumphant Towel
  
  
  
• 330 Points
  Glory Seeker
  Reward: Shortcake
  
  
  
• 360 Points
  Glory Seeker
  Reward: Giver's Beard
  
  
  
• 390 Points
  Myth Delver
  Reward: Durian
  
  
  
• 420 Points
  World Explorer
  Reward: Trapper's Crest
  
  
  
• 450 Points
  Ace Hunter
  Reward: Bandit's Mask
  
  
  
• 480 Points
  Legendary Redhead
  Reward: Wyrmpowder
  

*Currently on 3rd playthrough, will be filling in the proper Ranks as I go.

There are a few instances where you can earn an easy Rank.

Labyrinths
These are Given on completion, so once you've passed all 20 floors, that's a Platinum

Snowboarding
The Kappa in the well gives a fun way to get down the mountain, master his challenges and you'll have another Platinum.

Boss refights in the G-Colluseum
Remember Arch Shelob that gave you a bit of a hard time? Now you're level 30 and packing an arsenal, head over to the G-Colluseum and give it a 1-hit insta-platinum!

New Game +
You can rack in all the Boss platinums rather easily since all the boss fights are accessable from the start, You can also instantly get your Fight Rewards in the G-Colluseum and beating every fight using the G-Medal will get you something amazing... but that's another story.