It would be cool if the game was developed with the possibility of supporting a replay system in mind. Assuming the game logic ends up being deterministic, one could get away with just storing the random seed together with each player's (effective) inputs for each tick (maybe you could also store entity positions at fixed "keyframes" - maybe every 5 seconds for instance - to assist skipping to a particular point in a replay without having to watch everything that came before it). At the end of a match, the game could then give you the option to save the replay locally so you can watch or share it. Replays could also let you see other player's POVs.

Unbiased
   
SVG vers found in https://jiggmin2.com/forums/showthread.p...956&page=3 (post 41) I can't post SVG here anymore it seems
(Filename says Pr2 but can be applicable to Pr4 as well)

Should they be in PR4? A debate for the ages.

If PR4 only takes one thing introduced in PR3, I would love to see some sort of matchmaking lobby.
In PR2, you have to type in the chat what level you want people to search for, and they have to search for it if they want to see what it is.
In PR3, you can see all games being hosted and join whatever sounds fun.  Makes the process a lot quicker and you get to try out new stuff more easily! 

I wish levels showed the fastest time achieved on each level, and your personal fastest time on each level. It would be cool on campaign levels, but would be neat to see on other levels designed for speedrunning.

It's been suggested so many times for PR2, so I might as well request it for PR4. A block that acts just like the other basic blocks, but doesn't reset your spawn when you fall or hit a net! All of the unsafe blocks in PR2 can be altered in some way.

Please give us more tools for drawing rather than a circle. I'm thinking a square! I've noticed the size 1 circle brush on PR2 is rather finnicky, as it can create some blurry lines like this:

This is kind of a crazy idea that wouldn't really work if the game is trying to be really close to PR2 - the ability to aim any items anywhere. Shoot a Laser Gun in any direction, swing the Sword any way. You could get more wild with it and have items like a Super Jump act as a makeshift dash in any direction, or Teleport not being locked to a lateral angle. A feature like this would make Deathmatches more complex. You'd aim these items with a mouse, and there could be a crosshair for it.

Again, this depends on if PR4 wants to be pretty much just a "PR2 remake" or a new game entirely, expanding the mechanics of the series fundamentally. I personally would prefer the latter so that PR4 can get wild with its additions, but it's up to Jiggmin.

The ability to click and drag to place blocks in the level editor! I always wished PR2 had the ability to do this (In PR2, you have to move the mouse back and forth).

I think PR4 should have a way to change the hue of the Basic Blocks, to easily make levels more colorful!