In this talk, I will highlight two areas in gaseous astrophysics where exciting mysteries could be addressed with a high-resolution (R > 10, 000) FUV spectrograph. First, I will discuss how the low redshift (z ~0.1) Lyman-α forest observations (requiring space-based FUV with R > 10000) have challenged the most advanced cosmological simulations and defy physical arguments that work well at z > 2, as the amount of neutral hydrogen predicted is far larger in simulations than what is observed. I will show how including active black hole feedback can reconcile the amount of neutral gas by providing extra heating. These findings herald a significant paradigm shift for cosmological simulations and observations that target the low redshift IGM, however, more data is needed to disentangle the models. Second, I will zoom back to the local ISM, where a large FoV R > 10,000 FUV spectrograph could reveal molecular H2 in emission via the H2 fluorescent excitation lines. Such observations could illuminate molecular cloud lifecycles and uncover the origins of mysterious structures in our Galaxy.