Every 10 points is one level. Touch a snake with a lower level and it's out. A higher level takes you out. Equal levels: both go.
Reach level 100 in Jungle Basin and you warp to Ember Dunes (max 1,000, pickups ×10). Reach 1,000 and you warp to Star Void (max 10,000, pickups ×100). If you're eliminated you can restart the arena you reached at its starting level.
Venom knocks the target down 3 levels and slows it. Mines take out any snake, at any level. In Super mode you're on fire: invincible, faster, and you beat every level for 8 seconds.
Spiked walls and spike bars are deadly unless you have a shield or Super mode.