Thanks for the kind words! We were actually split internally on how far we wanted to take the references, but decided at least a few were warranted given the context of the jam. We're glad you agree and weren't put off by them!
Originally, we were going to have the spikes in pits in the ground, but ultimately they were made part of the main landscape and the concept of the player falling into a pit was dropped entirely due to time constraints. One of our team members was also confused by the spikes during playtesting, but we never went back to redo the sprite. We'll definitely keep this in mind for the future if we have a similar obstacle in a different game. It probably should have been something very traditional and obvious given the scope and speed with which we expected the player to adapt to each mode.
There actually isn't any health during the platformer, which in retrospect we could've probably made more obvious. The only real lose condition is touching the slug. All the other obstacles do is temporarily stun you. In an abstract way, your distance from the slug is kind of like your health bar.
The player always has full health at the start of every mode, but the slug's health left depends on whether you won or lost the previous round. For example, if you lose the shmup and the slug has half its health bar left, the next time you play the shmup, you will still be in the same "phase" as before and the slug will still have half health, but the player will have full health again. If you win in any mode, you will have been moved onto the next phase of the mode with a bump in difficulty, and the slug's health is fully restored. For the runner, since there is no health bar, we tracked how long you had played the runner and ensured that the player would pick up where they left off in terms of time (ex: if the runner is supposed to last 30 seconds and you lost 15 seconds in, you only need to survive another 15 seconds to win upon re-entering the mode).
Thanks again for playing! We really appreciated the thoughtful feedback!