If you still need help, these are the two ways i can think of doing this:
Simpler way:
I only just discovered this way so it might not work but i still feel it's worth testing:
First, add a 'message' block to any sprite apart from the players (I recommend using a new type of block) Then, make a block for the down arrow key sending a message (keep in mind message blocks and mailbox blocks are a way of blocks messaging eachother.) have a mailbox option on each of the sprites that respond to the same message sent from the other block that the 'message' block is in, make sure the mailbox block is after a number and a filter (What you aim to do is make a filter that works as a variable that decides which option to select, you do this by having a value increase whenever the down arrow or up arrow key is pressed which you can do with two number blocks, one adding onto the other block.)
Advanced way:
having an animation to first show if they've been selected such as making a highlight around the players for example, I would then have an invisible block (doing this I would have an animation without any textures so you can see the block you're moving). I would then have the block move it's position using the position command so for example when the down arrrow key is pressed, the block move down one, use on number block that has +32 and one number block that has 0 on in then join the +32 number block to the 0 using the out from the +32 to the + on the 0 block (I believe to move one square down, it would have to move down 32 pixles? I might be wrong.) It gets a bit complicated here: Using the 0 number block, attach it to a filter where it says 'in'. Make the filter value as low and as high as the screen goes (might need to test / research that). Then finally make the sprites trigger when they collide with this block using the 'Collision' block.
I will try to make a script that impliment both these features in which you can copy the code if you'd prefere but i only request that if i do this, that you credit me if thats ok.
Comments
http://flowlab.io/examples
The specific link to the Select screen example:
http://flowlab.io/game/play/815166
There's all the information you need.
Need more?
http://flowlab.io/resources
Simpler way:
I only just discovered this way so it might not work but i still feel it's worth testing:
First, add a 'message' block to any sprite apart from the players (I recommend using a new type of block) Then, make a block for the down arrow key sending a message (keep in mind message blocks and mailbox blocks are a way of blocks messaging eachother.) have a mailbox option on each of the sprites that respond to the same message sent from the other block that the 'message' block is in, make sure the mailbox block is after a number and a filter (What you aim to do is make a filter that works as a variable that decides which option to select, you do this by having a value increase whenever the down arrow or up arrow key is pressed which you can do with two number blocks, one adding onto the other block.)
Advanced way:
having an animation to first show if they've been selected such as making a highlight around the players for example, I would then have an invisible block (doing this I would have an animation without any textures so you can see the block you're moving). I would then have the block move it's position using the position command so for example when the down arrrow key is pressed, the block move down one, use on number block that has +32 and one number block that has 0 on in then join the +32 number block to the 0 using the out from the +32 to the + on the 0 block (I believe to move one square down, it would have to move down 32 pixles? I might be wrong.) It gets a bit complicated here: Using the 0 number block, attach it to a filter where it says 'in'. Make the filter value as low and as high as the screen goes (might need to test / research that). Then finally make the sprites trigger when they collide with this block using the 'Collision' block.
I will try to make a script that impliment both these features in which you can copy the code if you'd prefere but i only request that if i do this, that you credit me if thats ok.