Cubixx HD

Here's where you'll spend most of your time in Cubixx HD. Challenges are single levels where you only have one life to complete the specific requirement for each level and there are Bronze, Silver, Gold and Platinum requirements to meet to make things even more interesting. Platinum requirements are HIDDEN until AFTER you obtain them which can be a bit of a hassle since not knowing what the threshold is can make you fall short of it or really overshoot. Lucky for you, here's a list with the platinum requirements for each Challenge:

Rehab 1: Complete the level by only using a single line start to finish.
Size Matters 1: Create 6 lines over 1000 before finishing the level.
Gluttony 1: Clear 4 areas worth 140 before finishing the level.
Hurry Up 1: Finish the level in under 18 seconds.
Cubixx Killer 1: Kill all Mini Cubixx in under 40 seconds.
Land Rush 1: Platinum is to make 3 faces where you've removed over 92% of the surface.
Chaser Buster 1: Kill 60 Line Chasers.
The MEGA Line 1: Complete a 5,500 length line.
Surfing 1: Surf over 900.
Gotta Kill 'Em All 1: Kill all 10 Line Chasers in under 30 seconds.
Cling On 1: Spend over 2 minutes and 30 seconds caught by Homers before finishing the level.
Combo'd 1: Get 5 Combos of 6
Bright Spark: Score over 350,000 before finishing the level.
Lasrever 1: Get a high score of over 250,000 before finishing the level.
Survival 1: Survive for 5 minutes and finish the level.
Rehab 2: Complete the level by only using a single line start to finish.
Speed Freak 1: Complete the level in under 9 seconds
Size Matters 2: Complete 6 lines over 900.
Gluttony 2: Carve out 4 areas worth 100+.
Asteroid Shower 1: Score over 800,000 and finish the level.
Pacifist 1: Complete the level in under 40 seconds without killing any Mini Cubixx.
Hurry Up 2: Complete the level in under 40 seconds.
Chaser Buster 2: Kill 90 chasers.
Gotta Kill 'Em All 2: Kill all chasers in under 40 seconds.
Black Holer: Score over 300,000 and complete the level.
Power Hungry 1: Collect 20 power-ups.
Combo'd 2: 5 Combos of 6 before finishing the level.
Land Rush 2: Cut away 3 faces over 92%.
Cubixx Killer 2: Kill all Mini Cubixx in under 1 minute.
Power Hungry 2: Collect 30 powerups.
Speed Freak 2: Complete the level in under 18 seconds.
Survival 2: Survive over 2 and a half minutes and complete the level.
Lasrever 2: Complete the level in under 35 seconds with reversed controls.
Pacifist 2: Complete the level in under 1 minute and 23 seconds without killing any Mini Cubixx (same as Pac3).
Speed Junkie 1: Score over 300,000 and complete the level.
Cling on 2: Spend over 3 minutes and 30 seconds caught by Homers and complete the level.
Surging 2: Surf over 1,400.
The MEGA Line 2: Complete a 5,500 length line.
Rehab 3: As usual, complete the level in a single line.
Gotta Kill 'Em All 3: Kill all chasers in under 52 seconds.
Hurry Up 3: Complete the level in under 28 seconds.
Power Hungry 3: Collect 30 power ups.
Kaerf Deeps: Finish the level in under 17 seconds with reversed controls and maxed out speed.
Speed Junkie 2: Score over 600,000.
Cubixx Killer 3: Kill all Mini Cubixx in under 50 seconds.
Speed Freak 3: Complete the level in 20.
Pacifist 3: Complete the level in under 1 minute and 23 seconds without killing a single Mini Cubixx.
Asteroid Shower 2: Score over 800,000 and complete the level.
Survival 3: Survive over 2 and a half minutes and complete the level.
Finale: Last one! Complete the level while achieving the following 9 feats:

1-Biggest Area: 140+
2-Big Face Cut: 90%
3-Longest Line: 1000+
4-Score: 300,000+
5-Surfed: 15+
6-6X Combo: 1
7-Enemy Kills: 15+
8-Powers Collected: 10+
9-Time: Under 1:30

Thanks to ER777 for helping with part of the platinum award requirements!