Note some morphs from other mods won't have the abilities unless the creator of that mod added that feature into his mod. To access bosses you must have the configurable setting in the config file for boss morphs set to true. Even players and bosses, including mobs from other mods. In order to morph you must know how to open the Morph Menu and use it For it to work, you need Forge and iChunUtil, which can be found on our.
It gives the user the ability to morph into several of the Vanilla Minecraft Mobs and use these mobs abilities. On this page you can download a mod for turning into mobs for Minecraft 1.7.10 / 1.7.2.