This walkthrough contains 14 videos arranged as follows:

• Videos 1 through 5 (one per chapter) show everything that can be done without breaking the water pump. This includes level completion, secrets and collectables.
  
• Video 6 shows how to break and fix the water pump.
  
• Videos 7 through 11 (one per chapter) show how to complete the water drop levels and obtain all remaining collectables and secrets.
  
• Video 12 shows how to achieve the alternate ending.
  
• Videos 13 and 14 show all boss fights and all puzzle levels, respectively.

In addition to visiting every regular and secret level, 100% completion requires you to obtain all of the following collectables:

• Difficulty points, which are awarded for completing the more action-oriented levels. Up to four can be earned per level; to earn all four, you must complete the level on the hardest difficulty.
  
• Water drops, which replace difficulty points when the water pump is broken.
  
• Exploration points, triangle-shaped collectables that are found in hidden or hard-to-reach locations.
  
• Dialog springs, which provide backstory throughout the game. (I'm not sure if these count directly toward 100% completion, but all of them must be activated in order to obtain one of the exploration points.)

TIMECODES
0:00 - All Regular Level Exits
5:32 - Splitty Boss Battle
6:52 - A01 Secret Exit + A01.1
7:33 - A02 Secret Exit + A02.1
8:10 - A03 Secret Exit + A03.1
9:14 - A10 Secret Exit + A10.1 & A10.2 (partial completion)
10:42 - A14 Secret Exit + A14.1

TIMECODES
0:00 - Puzzle Levels
1:34 - Non-Puzzle Levels (Regular Exits)
5:51 - Mr. D.A.N.C.E. Boss Battle
7:31 - B03 Secret Exit + B03.1

TIMECODES
0:00 - Puzzle Levels
1:40 - Non-Puzzle Levels (Regular Exits)
10:48 - Mama Squid Boss Battle
12:31 - C01 Secret Exit + C01.1
15:09 - C13 Secret Exit

TIMECODES
0:00 - Puzzle Levels
3:23 - Non-Puzzle Levels (Regular Exits)
9:11 - Helpy Boss Battle
10:29 - D03 Secret Exit + D03.1
12:13 - D05 Secret Exit + D05.1 & D05.2
14:06 - D06 Exploration Point & Secret Exit + D06.1
15:12 - D06.2
16:45 - D06.3
18:39 - D06.4 (Tower Defense Boss Battle vs. Joe)
19:55 - D06.5
20:09 - D10 Secret Exit + D10.1

TIMECODES
0:00 - Puzzle Levels
2:04 - Regular Levels E05 to E09
4:30 - Bartender Boss Battle (E10)
5:18 - Regular Levels E11 to E13
6:27 - Bartholomew Boss Battle (E14)
6:40 - Regular Levels E15 & E16
7:59 - Squid Boss Battle Phase 1 (E17)
9:42 - Squid Boss Battle Phase 2 (E18)
10:39 - Regular (Bad) Ending (E19)
11:27 - Level Hub Exploration Point
12:10 - E03 Secret Exit + E03.1
13:00 - E06 Secret Exit + E06.1
16:14 - E15 Secret Exit + E15.1 & E15.2
17:55 - E19 Secret Exit + E19.1

TIMECODES
0:00 - All Water Drops
3:57 - Underwater Splitty Boss Battle
5:44 - A10.2 Final Collectables

TIMECODES
0:00 - All Water Drops
4:57 - B18 Exploration Point + Underwater Mr. D.A.N.C.E. Boss Battle

TIMECODES
0:00 - All Water Drops
4:34 - No-Water Mama Squid Boss Battle

TIMECODES
0:00 - Secret Level Water Drops
4:10 - Underwater Tower Defense Boss Battle (vs. Joe)
5:34 - Regular Level Water Drops
11:37 - Underwater Helpy Boss Battle

TIMECODES
0:00 - E07 to E09 Water Drops
1:03 - E10 Exploration Point + Underwater Bartender Boss Battle
2:11 - E11 to E13 Water Drops
3:22 - Underwater Bartholomew Boss Battle (E14)
3:33 - E15 Water Drops
4:02 - Secret Level Water Drops
5:17 - Underwater Squid Boss Battle Phase 1
6:11 - Underwater Squid Boss Battle Phase 2

TIMECODES
0:00 - Alternative Ending walkthrough
4:56 - Post-credits hub collectables
5:49 - B04.2 secret exit + B04.4 exploration point
6:55 - E19 exploration point

TIMECODES
0:00 - Splitty - regular version (level A20)
0:45 - Splitty - underwater version (level A20 pump reversed)
2:22 - Mr. D.A.N.C.E. - regular version (level B18)
3:32 - Mr. D.A.N.C.E. - underwater version (level B18 pump reversed)
4:54 - Mama Squid - regular version (level C21)
6:12 - Mama Squid - no water version (level C21 pump reversed)
7:01 - Joe (tower defense smiley boss) - regular version (level D06.4)
8:17 - Joe - underwater version (level D06.4 pump reversed)
9:22 - Helpy - regular version (level D19)
10:11 - Helpy - underwater version (level D19 pump reversed)
11:43 - Bartender - regular version (level E10)
12:31 - Bartender - underwater version (level E10 pump reversed)
13:38 - Bartholomew - regular version (level E14)
13:50 - Bartholomew - no water version (level E14 pump reversed)
14:01 - Squid, phase 1 - regular version (level E17)
15:43 - Squid, phase 1 - underwater version (level E17 pump reversed)
16:34 - Squid, phase 2 - regular version (level E18)
17:30 - Squid, phase 2 - underwater version (level E18 pump reversed)

TIMECODES
0:00 - Chapter B regular puzzle levels (B01 to B03)
1:29 - Chapter B secret puzzle level (B03.1)
2:27 - Chapter C regular puzzle levels (C01 to C03)
3:57 - Chapter C secret puzzle level (C01.1)
6:18 - Chapter D regular puzzle levels (D01 to D04)
9:32 - Chapter D secret puzzle levels (D03 secret exit + D03.1)
11:12 - Chapter E regular puzzle levels (E01 to E04)
13:09 - Chapter E secret puzzle levels (E03 secret exit + E03.1 + E06.1)