Main-group chemistry has grown remarkably in recent decades, as highlighted in several reviews. In 2010, Power drew attention to 'Main-Group elements as Transition Metals'. Since then, significant progress has been made in main-group chemistry, including metallylenes. Key reviews include the works in 2018 by by Hadlington, Drieß and Jones, titled 'Low-valent group 14 element hydride chemistry: towards catalysis', and Chu and Nikonov's 'Oxidative Addition and Reductive Elimination at Main-Group Element Centers'. More recent (mini)reviews are 'Small molecule activation by welldefined compounds of heavy p-block elements' by Oberdorf and Lichtenberg, 'Applications of low-valent compounds with heavy group-14 elements' by Akhtar, Gaurav and Khan, and 'Heterocyclic heavy analogues of carbenes: structure and chemical properties. by review.' by Arsenyeva and Piskunov, and 'Recent advances in the chemistry of isolable carbene analogues with group 13-15 elements' by He et al. Therefore, this feature article aims to contribute to this field by providing insight into the recent developments of metallylenes and their reactivity, with a particular focus on ligand effects, electronic structure, and mechanistic pathways. First, we will examine small molecule activation with particular emphasis on the effects of varying the Group 14 tetrel element -varying from silylenes to germylenes to stannylenes to plumbylenes -and the influence of different ligands. Next, we will focus on the reversibility of small molecule activation and follow-up reactions. Finally, we will end with a section on the challenges associated with metallylenes.