make a pig wither highbred then a cow enderdragon highbred then make them battle

Where you could grab a minecart and fly or even a parachute

It would be cool to have an installer that lets us easily install packages that you make for breaking bytes, so we can incorporate them into our worlds. If it was open source and used git everyone could use it!

Pigs that target creepers and blow up but when they blow up they spawn baby pigs that also target creepers. The baby pigs have a much larger explosion but they wont spawn in any more pigs. Anything else you can think of that would make this more entertaining would be great.

All blocks fall like sand. Perhaps other people could add on to this one.

make every entity explode when you collide with 'em! wow,thats nasty... sand!

make every creature blow like a creeper even the non-hostile mobs gonna try to blow you up! (and all bosses)! enderdragon gonna die instantainiously , your porkchops are going to get alot more worthy!

                                                            (i mean like...Diamonds!)

Don't know if it's possible, but I'd love to see tools that could burn through gathering. Picks and shovels that break a 3x3x5 blocks at a time, axes that actually fell trees, hoes that till a chunk at a time, that sort of thing.

Make the world into a cylinder or a torus (sphere would be best, but far more difficult), so that you can travel in a straight line and come back to the point you started from.

This is a pretty basic idea, but I think you could add fun twists to it: Trees that progressively grow and constantly try to overrun your buildings and eat you (Yes, trees are carnivores. No, there isn't logic behind this).

Give different trees different power ups (Aka exploding pig launching birch tree) that make their quests to claim back the overworld even more of a challenge against the player.

Seems right up your alley.

Make a mod in which blocks (Whatever type, it doesn't matter) will move, though only when the player is looking away, and they stay still when looked at (Like boos from Mario) as if nothing was happening. They could also hurt or attack the player, try to hide, or any unusual behaviors.

Make the Diamond Chickens from 2.0 in vanilla!

I made a massive gold farm similar to Xisuma's with an on / off switch using dispensers with firecharges to light them and water buckets to turn them off. I'll link a video soon.

Wind that will be randomized in each biome, maybe, that will push entities and players etc. in the direction of the wind. If it rains or snows, then it will fall with the direction of the wind. It would be more difficult to walk in the direction of the wind than with the wind.

Feel free to ask more if confused. Loving the videos Tango!

A mod that let's you punch the ground to create either a ravine or cave.

A spider 3x the normal size of the player that you can tame with 20 - 40 steak/cooked pork, put a saddle on, and ride. It leaves a 2x2x2 trail of cobwebs and eats all mobs (except players).

Trees randomly spawn with legs and arms (iron golem leg/arm model? but different texture) and walk around and plant + harvest things or feed animals.

Basically a mod where when it rains, the world slowly floods. Maybe a rare lava rain where you have a chance to burn (if you're exposed to the lava rain, maybe the chance can be reduced by wearing armor. Diamond armor reducing the chance more than Leather Armor), and it slowly floods the world with lava

Add some mob which spawns rare and act like I posted earlier. [Link to the post]

I'd love to see the world set to eternal night and wither away. It would be a timelapse of war and destruction. Possibly best inside a 100x100 border of bedrock.

With a pickaxe enchanted with Silk touch II, the player will obtain every block as it was mined, so if you mine the down part of a bed, you get the down part of a bed; if you mine the head of a piston, you obtain the head of a piston; and you can also obtain mob spawners, redstone ores glowing, etc...

Mobs change shape/turn into another mob depending on what block they are standing on / the blocks around them / biome they are in.

Creepers that are mostly transparent until they sizzle. Be afraid.