Here is a selection of Ultra Monster illustrations done by Takayoshi Mizuki between 1965 and 1972.



Ultraseven vs. Aron



Ultraman vs. Gabula & Rigger



Alien Goron vs. Gumonga



Kaiju Ebanashi



Alien Godola, Alien Borg, Alien Baltan, Alien Zarab, Alien Icarus, Alien Bado



Eleking, Dino-Tank



Capsule Monsters: Windam, Agira, Miclas



Ultraseven



Alien Baltan // Magular



Garamon // Kanegon



Litra & Gomess // Peter & Todora



Ultraseven, Alien Icarus, Alien Pega, Alien Cool



Ultraseven, Bostang, Starbem Gyeron



Kaiju Ebanashi



Ultraman vs. Jirass



Seabozu & Zaragas



Peguila & Kanegon



Jamila & Alien Mephilas



Kaiju Ebanashi



Aboras, Banila, Zambolar



Ultraman vs. Jamila



Ultraman, Alien Baltan, Bemular

[Link: Takayoshi Mizuki]