Never mind, turns out the levels are just not saved as a "Level Up" item, but adjust relative to the total amount of cells eat:cells needed for level up
There appears to be an issue with leveling, where, once you take a level, the level to the immediate left of it, whether in progress or complete, will be exhausted as well.
Gamebreaker combo: Shorter Worm+ Sleek Spikes+ Blood Fangs+ Shredder Mouth+ Either of the final upgrades. You never hit the ground and get ridiculous combos at the end with no distinct risk of death.
There'r enough people complaining about the economy, so I'll just express complaint with how the final dungeon rather readily jumps ahead in terms of difficulty compared to any other levels of the map. Before I was fighting in it, I would get, on average, 69% for my medium chance to hit. In the last dungeon, I was lucky to get 60% for my light attack. There's seriously an unbalanced damage ramp in this level.
Lemme correct my previous opinion: Max the second flyer. That gets you to eleven. Then, max the mines, and use them to bomb ground-to-air defenses, and, lastly, level out the first flyer for dedicated anti air (Less distracted by ground units)
 "Reprisal"){kind=icon}
 "Deep Sleep"){kind=icon}
 "Bloons TD 5"){kind=icon}
 "Hexcelle"){kind=icon}
 "The Sandbox"){kind=icon}
 "Effing Worms 2"){kind=icon}
 "Arkandian Revenant"){kind=icon}
 "The King's League"){kind=icon}
 "Vector Stunt"){kind=icon}
 "Alienocalypse"){kind=icon}