[quote=@OtomostheCrazy]
[@Lugubrious]

What kind of amphibian is it, anyway?
[/quote]

The version of Aforgomon attacking them has amphibian traits, namely its skin and a head inside its mouth, such as the Demon of Song here:

[img]http://img2.wikia.nocookie.net/__cb20140314141009/darksouls/images/4/4c/Demon_of_Song.png[/img]

Though it still has the bipedal body shape.