The Entity Supreme always learns. He learns to appease those who could be useful to him, he learns how to take advantage of newly forged partnerships, and he learns how to construct better vessels for the Great Ones. The Dun'dath mech is perfect for Aphoom-Zhah. Capable of lightning-fast movements and deadly long- and short-range attacks, the mech's main feature is its ability to channel Aphoom-Zhah's ice-cold flame through the 7 cannon-ports and the maw. The Entity has given Aphoom-Zhah the perfect payment for His services, something he never could have had: the physical form of His dreams.
There is one other feature that came as a bonus for Aphoom-Zhah: the charge-shield coming from the bottom of the Dun'dath mech's chest is a channel for a mixture of Aphoom-Zhah's flame and willpower - the perfect way for him to create followers, just like Hastur. But the difference is that it doesn't take nearly as much effort for Aphoom-Zhah. His legions are limitless, and they aren't as self-reliant as the Hounds of Hastur. They can worship all they want, their culture will prosper, but they will fearlessly leap into battle if Aphoom-Zhah commands it.