On Maker-Breaker domination game critical graphs

Abstract: The Maker-Breaker domination game is played on a graph $G$ by Dominator and Staller who alternate turns selecting an unplayed vertex of $G$. The goal of Dominator is that the vertices he selected during the game form a dominating set while Staller's goal is to prevent this from happening. The graph invariant $\gamma_{\rm MB}'(G)$ is the number of Dominator's moves in the game played on $G$ in which he can achieve his goal when Staller makes the first move and both players play optimally. In this paper, we continue the investigation of $2$-$\gamma_{\rm MB}'$-critical graphs, initiated in [Divarakan et al., Maker--Breaker domination game critical graphs, Discrete Appl.\ Math. 368 (2025) 126--134], which are defined as the graphs $G$ with $\gamma_{\rm MB}'(G)=2$ and $\gamma_{\rm MB}'(G-e)>2$ for every edge $e$ in $G$. The authors characterized bipartite $2$-$\gamma_{\rm MB}'$-critical graphs, and found an example of a non-bipartite $2$-$\gamma_{\rm MB}'$-critical graph. In this paper, we characterize the $2$-$\gamma_{\rm MB}'$-critical graphs that have a cut-vertex, which are represented by two infinite families. In addition, we prove that $C_5$ is the only non-bipartite, triangle-free $2$-$\gamma_{\rm MB}'$-critical graph.