From 猫(ねこ) (neko) + 戯(じゃ)らし (jarashi, 連(れん)用(よう)形(けい) (ren'yōkei, “stem or continuative form”) of the verb 戯(じゃ)らす (jarasu).).
ねこじゃらし • (nekojarashi) ←ねこじやらし (nekozyarasi)?