Amazing!

Aliens to use for each level and when to purchase upgrades 1-1 - Swampfire 1-2 - Swampfire. Then buy Echo Echo's YYY attack and "A" charge attack 1-3 - Echo Echo 1-4 - Echo Echo 2-1 - Echo Echo 2-2 - Goop 2-3 - Swampfire 2-4 - Swampfire 3-1 - Goop. Then buy Swampfire's YYA attack 3-2 - Swampfire 3-3 - Goop, then Echo Echo. Then buy Swampfire's Max Health. 3-4 - Swampfire 4-1 - Goop 4-2 - Swampfire. Then buy Chromastone's YYA attack and "A" charge attack 4-3 - Chromastone 4-4 - Swampfire