Sigma Posting (Follow on BS)さんのイラストまとめ

Sigmastar

Source: Sunstar
Mega Man V (Gameboy) by Minakuchi Engineering

Sigma face edited from sprites provided by @hansungkee1 and Aburtos

Black Sigolem

Source: Black Golem
Koumajou Densetsu II: Stranger's Requiem (PC) by Frontier Aja

Sigmutoid Man

Source: Mutoid Man
Super Smash TV (SNES) by Beam Software

Sigmastoth

Source: Castoth
Illusion of Gaia (SNES) by Quintet

CATSIGMA

Source: CATS
Zero Wing (Genesis) by Toaplan

Monster-SiGma

Source: Monster-G (Ver 1.03 revision)
The Revenge of Shinobi (Genesis) by Sega

@themmnetwork You know who else is Irregular?

Sigmah'lar

Source: Kh'lar
Skyblazer (SNES) by Ukiyotei

Sigmario

Source: Mario
Super Mario Bros. 3 (NES) by Nintendo EAD

Sigumaro

Source: Yeti (Umaro)
Final Fantasy VI (SNES) by Square