Bloons TD 6 - 1 Tower Only Challenge but on an Expert Map...
There is an in-game achievement called All for One and One for One, where only one tower is allowed on the map at any time. A challenge a fellow community member made was to do this achievement on the 'Expert' map Infernal!
Music:
More Plastic - Rewind
Cristina Vee & Obadiah Brown-Beach - ALIVE