I don't like auto pad from screen edges myself. Adding keys for moving is a given though 👍
The skulls spawn when you go far enough in any direction and their amount increases the further you go. So they're a means to end the runs and prevent from going infinite. They also spawn in other possible spots you could have placed your previous bone.
I did think of auto discard but it does have some issues that made me not add such a mechanic. It couldn't be automatic if there are multiple bones in hand. It also tells the player there is a possible move if it doesn't happen.