These are all creatures referred to in “The Mound”, that used to populate the ruins of N’kai and the abyss of Yoth. The first image corresponds to the extinct Ghasts of N’kai that, like the Dreamlands Ghasts, spawned from a junction with Zin.
The second image corresponds to the ancient inhabitants of Yoth, the Yothan Archosaurs, that probably interacted with serpent folk, formless spawn and other ancient beings devoted to Tsathoggua. These are also extinct as per the Ancients of K’n-yan’s records.
The final image corresponds to the Gyaa-Yoth, an unnatural hybrid that resulted of genetic exchange between Ghasts and Yothans. These submissive creatures are more resistant to light and can survive as slaves and beasts of burden in the blue-lit caverns of K’n-yan. Unlike their ancestors, Gyaa-Yothn are not extinct.
Also, please note that the extinct creatures above are not full-body images because they are not described in the text.