  In this paper, we study all ways of constructing modular compactifications of
the moduli space $\mathcal{M}_{g,n}$ of $n$-pointed smooth algebraic curves of
genus $g$ by allowing markings to collide. We find that for any such
compactification, collisions of markings are controlled by a simplicial complex
which we call the collision complex. Conversely, we identify modular
compactifications of $\mathcal{M}_{g,n}$ with essentially arbitrary collision
complexes, including complexes not associated to any space of weighted pointed
stable curves. These moduli spaces classify the modular compactifications of
$\mathcal{M}_{g,n}$ by nodal curves with smooth markings as well as the modular
compactifications of $\mathcal{M}_{1,n}$ with Gorenstein curves and smooth
markings. These compactifications generalize previous constructions given by
Hassett, Smyth, and Bozlee--Kuo--Neff.
