Ultracold two-dimensional (2D) Bose gases exhibit behaviour that differs markedly from their three-dimensional counterparts, making them a sensitive setting for studying symmetry and interaction effects.In the idealized Gross-Pitaevskii equation (GPE), scale invariance gives rise to unique phenomena such as Townes solitons, 'strong' self-similar collapse, and interaction-independent breathing-mode frequencies intightly trapped systems. However, realistic bosonic systems exhibit a strong quantum anomaly, namely, a breaking of scale invariance and, in consequence, the formation of universal droplets. It remains unclearwhether a simple, unified theoretical framework exists to analyse these phenomena. To address that, we introduce a density-dependent coupling into the GPE, which successfully describes this behaviour, whilepreserving a structure suitable for intuitive analytical and numerical exploration.In this talk, I will focus on the mathematical structure of the Gross-Pitaevskii description of attractive 2D Bose gases. I will discuss the origin and consequences of scale invariance, its breakdown in realisticsystems, and the limitations of the standard GPE. I will then show how these limitations can be overcome using a generalized GPE, and how this framework connects collapse dynamics, Townes solitons, and self-bound droplets. The lecture will emphasize analytical arguments, scaling properties, and their relevance for current experiments.