Damage **and** oxygen. I thought that sounded too complicated for my take on the diving game. The cracked dome mechanic works really well, with the extra screen width, and letting the player wrap around the edges adds another dimension or half. I found just L and R worked best for steering my free fall. I only scored 275 that way...
I liked how there was no story or instruction and it all just falls into place with trial and error. Reading the comments after playing indicates I was on the right track, but a leaderboard would have let me know how hard I had to push
After reading comments I discovered the attack mechanism and extended my run a bit to 475, having to choose whether to kill jellys or scavenge platforms.