My suggestions for Mcreator.

 So i have 3 suggestions that I think will help a lot in some mods.

1. A new option next to the "is water entity" box for semi aquatic mobs. The option would be obviously titled "is entity semi-aquatic(or something along the lines of that)" and this would allow for the entity to move like a normal land entity on land and swim like fish under water. There could also be a place where you could set the movement speed for the swimming. Either this idea or make the "swim randomly with speed [ ]" block be able to do this in AI and goals, although that would probably only work if there is already a "move randomly(enables walking) with speed [ ]" block in it's ai. The same thing should go for if you want to make a mob that can fly but still walk.
2. A new block in Entity data procedures called "Replace [event/target entity] with (insert drop-down menu to select entity) keep NBT data [true]." This block would allow for an entity to be replaced with another entity while still keeping the NBT data(name, health, potion effects it has, etc.) of the previous entity, something that isn't really possible in the base Mcreator. Sure, you could use local variables, but those do have it's restrictions. This wouldn't replace the "despawn [event/target entity]" block for obvious reasons, however.
3. When making a block, custom tool elements(like tools that you make that aren't of the given categories sword, pickaxe, axe, spade, etc.) Should be an option when choosing the tools that will be able to break it.

So yeah, das all i wanted to suggest :D