Add a lava block that will deal damage when touched but it won't kill you instantly instead it will deal the player 6 points of damage so it gives them a chance to get back up if they fall. As for how it will look you could just use the same skin for water instead of replacing the blue with orange and the white with yellow.
We are already able to "make" lava, we have spikes, just put red plastic over them. Also, 6 damage seems kinda...unreal, you know? If you fall in lava, you can just be like "Ow! That hurt!" and walk out. You would die.