de Blob itself is a pretty simple game, and its achievements are largely self-explanatory as well. Hence I won't going into too much detail about all the achievements. I mainly wrote this guide for the stuff in levels 9 and 10, but will briefly go over all the achievements as well.
Also, there are already other guides out there for the console versions and everything written in those applies to the Steam version as well.

de Blob's 23 achievement break down as follows:

• 10 storyline (one for each story level)
  
• 11 in-game awards
  
• 1 secret missions
  
• 1 'platinum' (unlock all other achievements)

These are awarded on the results screen on completion of a level. One achievement per level, ten levels = ten achievements.




🏆 Last Resort's savior - Save Last Resort from INKT Corporation.
🏆 Uptown's savior - Save Uptown from INKT Corporation.
🏆 Downtown's savior - Save Downtown from INKT Corporation.
🏆 The Chroma Dam's savior - Save the Chroma Dam from INKT Corporation.
🏆 Guggentraz Island's savior - Save Guggentraz Island from INKT Corporation.
🏆 The Docklands' savior - Save the Docklands from INKT Corporation.
🏆 Hanging Gardens' savior - Save Hanging Gardens from INKT Corporation.
🏆 Chroma City Fun Park's savior - Save Chroma City Fun Park from INKT Corporation.
🏆 Ministry of Ink's savior - Save Ministry of Ink from INKT Corporation.
🏆 World savior - Defeat INKT Corporation.

Each level has 10 awards. 10 levels of 10 awards equals 100 awards. All 100 are needed for the achievements. Awards themselves are related to your performance in each level.

% Painted
Paint the level 100%. Only objects that give 100 points (or more) count towards this total.
▪️ Unlock this award in every level for 🏆 Da Vinci - Paint everything... e-ve-ry-thing!


Challenges
These are designated by giant hand arrows. Different colours are different types of challenges. Challenges can be replayed if failed.
▪️ Unlock this award in every level for 🏆 Rocky - Defeat'em all.

Time
Complete the level as quickly as possible.
▪️ Unlock this award in every level for 🏆 Chronos - Run to defeat the time.


Styles
Collect all Styles. These are purple collectibles scattered around the level.
▪️ Unlock this award in every level for 🏆 Prada - What a style!


Trees
Paint all trees. Uncoloured trees are just a stump until coloured. Transforms will usually paint a bunch of trees but some are quite hidden.
▪️ Unlock this award in every level for 🏆 Edward Scissorhands - Decorate all trees.

Landmarks
All these are completed from challenges. Landmarks are the buildings that need to be injected with paint.
▪️ Unlock this award in every level for 🏆 Shaken, not stirred - Shake! Shake! Shake!

Billboards
Paint all billboards. They're usually hanging on buildings or on top.
▪️ Unlock this award in every level for 🏆 Cinema Usher - Prepare the billboard.


Transforms
Transforms are the green balls that paint a wide area. Activate them by slamming them.
▪️ Unlock this award in every level for 🏆 Transformers - Optimus paint engine.


Raydians
Paint a city block to release Raydians. Released Raydians are always in groups of eight, but some are also scattered around the level.
▪️ Unlock this award in every level for 🏆 Braveheart - They may take away our colour, but they'll never take our freedom!

Blimp
The blimp flies in a predetermined path over the entire level. Climb up high and jump to it to paint it. Can be hard to spot due to the poor camera.
▪️ Unlock this award in every level for 🏆 Icarus - To blimp and beyond!

Note: The compass will show the location of the nearest Challenge or Transform. After clearing all the challenges and transforms in a level, it will show objects missing for % Painted. Keep this in mind as this will be vital for the % Painted award.

The 11th achievement related to awards is 🏆 Gold seeker - Get all gold medals in story mode. The medal awarded is tied to the score, with bronze being the minimum required to finish a level. There isn't much need to worry about the score and medals, it's nigh on impossible to miss this when going for the other awards.

Complete each level getting every award except the Time Trial awards, so that's 9 awards per level.

The first eight levels are fully backtrackable, so be sure to complete everything before finishing the level. Progress can be tracked from the pause menu. Generally the time limit isn't much of an issue, though even if it runs out you only lose a life and are given another five minutes.

On the off chance that you don't finish a level with 9 awards, you can replay the level for only the award(s) you missed. That said, always finish the more time consuming awards like % Painted as progress isn't saved (this includes collectibles).

Be warned that each level is quite long, usually upwards of a an hour and there's no saving mid-level. Quitting at any point before entering the exit pool means the level will need to be played from the beginning next time.

Note how I said the first eight levels, unfortunately the last two have points of no return.

The large bridge is the point of no return in this level. Crossing it beyond the extra life will cause it to collapse. Before crossing the bridge make sure your stats are as follows (plus the blimp):

• 88% painted
  
• 14/15 trees
  
• 72/72 raydians
  
• 15/17 billboards
  
• 14/16 landmarks
  
• 2/3 transforms
  
• 15/17 challenges
  
• 11/13 styles

It's easy to know if everything so far is painted correctly because the bump at the beginning of the bridge will push the percentage from 87% to 88%. It's painted blue in the screenshot below.



There are two points of no return in the final level. The first is using the z-jump to jump onto the spaceship. Your stats at this point will be as follows (plus the blimp):

• 50% painted
  
• 26/26 trees
  
• 24/24 raydians
  
• 2/2 billboards
  
• 3/10 landmarks
  
• 0/1 transform
  
• 6/6 challenges
  
• 6/13 styles

It's hard to tell if everything is painted correctly, so be sure to use the compass to double-check that everything is painted (since all the challenges are completed).

As a general indication, the screenshot below has exactly 50% painted. Everything not pictured behind is painted and note that the left silo, pipes, and two z-jump platforms are unpainted (the ships don't count).


As pointed out by Riverspoke:

When you're at the rear thrusters of the ship, you should have mentioned NOT TO DO THE LANDMARK BEFORE GETTING THE STYLES. Because after doing the landmark, the place gets filled with ink and one of the styles is locked out forever. You doomed me and I had to restart the level.

The missable style is one of the two styles on the high platforms reached by z-jumping from the panel outside the hole.

The second point of no return is the gate leading to the final boss. Every award (except the single transform) should be complete and 95% painted. Again, use the compass to double-check.

At the final boss, beware that the boss can 'unpaint' the two spires either side of the gate with ink blasts. The 100% painted notification is shown immediately on painting the final fuel rod (hexagonal platform). If it doesn't show maybe you can still go back and check the two spires are painted (before slamming the final transform), but the rest of the level is closed off.

Replay every level this time solely focusing on going quick for the Time Trial awards. Only the bare minimum needs to be done to open all the gates, and then the exit pool. Everything else can be skipped. As soon the bronze medal unlocks, the level exit is unlocked.

Opening gates is tied to the score, so it's better to just do easy challenges (like races, landmarks, enemy kills) and paint entire building blocks at a time for the bonus. The levels should be familiar enough by now, so they shouldn't cause any trouble. The times themselves are quite generous and I usually had ~5 minutes left over.

The time limits are:
Level 1 Last Resort - 8:00
Level 2 Uptown - 13:30
Level 3 Downtown - 20:30
Level 4 The Chroma Dam - 18:00
Level 5 Guggentraz Island - 17:00
Level 6 The Docklands - 28:00
Level 7 Hanging Gardens - 25:00
Level 8 Chroma City Fun Park - 17:00
Level 9 Ministry of Ink - 24:30
Level 10 Lake Raydia - 27:00

On the final level, only 90,000 points are needed which can be gotten before jumping on the spaceship. That means the entire spaceship section can be skipped and can just beeline to the final boss. I ended needing less than half the allotted time.

Completing a level unlocks two additional quests for each location. These are basically the same as the challenges in the story mode except they're set in their own stage. A gold medal is awarded for fully completing the task and reaching the exit pool within the time limit.

Each will probably take a few attempts to learn the location of the objects and the correct path to take, but they're all very lenient with time except one - Sinking Feeling in Lake Raydia which will have seconds/milliseconds left on the clock.

Below is a video of all the secret missions courtesy of iPlay Retro:

In addition to the 10 gold medals earned during the story, getting gold in every secret mission will unlock 🏆 Olympic Games - Earn 30 gold medals.

And finally if that was your last achievement, 🏆 King Blob - Master De Blob in all possible ways.