Since it's the weekend and I don't have work I was able to spend most of day 5 on this, rather than just a few hours in the evening, so I got loads done!
The first thing I did was make it so that you can actually reel in the fish, crab and squid. The jelly and it's stingers can't be hooked (in fact, I added collision to the jelly body so the hook can't even pass through it - color coding, hooray!). I also set up a proper level loading system so I can design levels in PICO-8's map editor then jump to them with load_level(n), with all the collision and creatures etc. set up and ready to go.
Now that my reel mechanic was fully functional it was time to move on to each creature's unique ability. The first one I did was the fish. When the fish collides with a jelly's stingers it is killed and becomes a skeleton (tricky to draw!). The skeleton can then be hooked and will cut off any stingers that it hits (including all attached stingers below the cut point). To demonstrate this I made the level shown in the gif above, which will be the first level that has both fish and jellies.
I don't want to explain any of the mechanics to the player; I want to design levels which introduce each mechanic in such a way that the player naturally discovers the functionality, consequences and combinations for themselves. Part of that is about forcing the player to think. I designed the level above so that you are immediately confronted with choice. The solution plays out the same whether you take the top or bottom fish and whether you cut the top or bottom row of stingers. But because the player has to make those small choices, it forces them to actually think about the situation and therefore (hopefully) fully understand what is happening and feel clever for finding the solution.
The second creature was the crab. There are now debris tiles which the hook can fit through but through which fish and squid cannot be dragged. Dragging a hard crab through them will smash the debris and open up new paths. Again, for this introductory puzzle there is only one simple solution but the player is confronted with choice. They can immediately hook the crab, but then when they try to grab the fish they'll find it won't fit through the debris. The only other possibility is to try dragging the crab through, and now the player feels smart because they discovered this mechanic on their own.
Tomorrow I'll be doing the final creature; the squid will leave an impassable ink trail for the first [insert number here] moves after being hooked. The only other mechanic I had planned was that reeled-in crabs would decrease your maximum line length (claws + fishing line = bad). This was meant to discourage the player from starting a level and always going for crabs first to clear out pathways. It's about making them think. I'll implement this if and when I find a need for it. With those done the gameplay mechanics will all be finished and it just becomes a question of how many interesting combinations and levels I can create! I'd also like to do nice menus and a title screen. I'm very happy with the design and aesthetics on this project, so I think I'll likely continue working on it post-jam and do more levels, more pixel art, cool visual effects and add sound and music (something I don't think I'll have time for tomorrow).