The transformerless modular multilevel DC/DC converter (MMC-DC) has been extensively investigated as an alternative to the isolated front-to-front MMC DC/DC converter. The absence of a transformer, which is typically the bulkiest component, makes it an attractive solution, especially in applications where available space is scarce. An MMC converter consists of multiple arms. Each arm is made up of submodules (SMs), which can be either half-bridge (HB) or full-bridge (FB). The types and total ratings of the submodules included in the arms are design choices. This paper presents a comprehensive analysis and comparison of various arm configurations for the transformerless MMC-DC converter operating at high step-down ratios. To support this, a theory of hybrid arms-i.e., arms that include both types of submodules-is developed and verified using a Simulink model. The results show that energy constraints in hybrid arms limit their advantages over fully FB or HB arms.