I have completed the list of Amphibian pieces out to the third perimeteer on a cubic board. I am still interested to know of any beyond that. They are as follows. Blanks indicate a cpompound that is still bound.
1 in 9 squares 1 in 27 cubes 3:0:0 Trebuchet
1 in 18 squares 1 in 54 cubes 3:3:0 Tripper
1 in 27 squares 1 in 81 cubes 3:3:3 Zombie
1 in 2 cells
1:1:0 Ferz
Frog
Paddick
2:1:1 Sexton
Senetoad
Seecillian
3:1:0 Camel
Canetoad
Caecillian
3:2:1 Fortnight
Fonetoad
Foecillian
1 in 4 cubes
1:1:1 Viceroy
Bullfrog
Natterjack
3:1:1 Elf
Leiopelma
Leptodactyl
3:3:1 Underscore
Nuiopelma
Nuptodactyl
1 in 4 squares or subset 1 in 8 cubes or subset
2:0:0 Dabbaba
Toad
2:2:0 Elephant
Newt
2:2:2 Eunuch
Eft
Extending to the 4th perimeter requires adding those pieces replacing:
Ferz/Sexton/Camel/Fortnight with Nimel/Arbez/Effarig - names derived e.g. Nimel+Trebuchet=Ninetoad;
Dabbaba/Elephant/Eunuch with Cobbler/Charolais/Srene/Commuter/Nhirolais/Corpse, as yet unnamed (unless you know better).
Extending to the 5th perimeter requires adding those pieces replacing:
Ferz/Sexton/Camel/Fortnight with Zemel/Monk/Gimel/Sustainer/Votary/Epoletna names derived e.g. Zemel+Trebuchet=Zenetoad;
Viceroy/Elf/Underscore with Exorcist/Oddfellow/Fieldmouse/Feaster/Broadwayman names derived e.g. Exorcist+Trebuchet=Xeiopelma;
Trebuchet/Tripper/Zombie with Quibbler/Quitter/Skeleton., as yet unnamed (unless you know better).
Trebuchet+Quibbler, Tripper+Quibbler, Zombie+Quibbler, Trebuchet+Quitter, Zombie+Quitter, Trebuchet+Skeleton, Tripper+Skeleton are also amphibious and also as yet unnamed (unless you know better).
1 in 27 cubes
3:0:0 Trebuchet
1 in 54 cubes
3:3:0 Tripper
1 in 81 cubes
3:3:3 Zombie
1 in 8 cubes or subset
Ferz/Sexton/Camel/Fortnight with Nimel/Arbez/Effarig - names derived e.g. Nimel+Trebuchet=Ninetoad;
Dabbaba/Elephant/Eunuch with Cobbler/Charolais/Srene/Commuter/Nhirolais/Corpse, as yet unnamed (unless you know better).
Extending to the 5th perimeter requires adding those pieces replacing:
Ferz/Sexton/Camel/Fortnight with Zemel/Monk/Gimel/Sustainer/Votary/Epoletna names derived e.g. Zemel+Trebuchet=Zenetoad;
Viceroy/Elf/Underscore with Exorcist/Oddfellow/Fieldmouse/Feaster/Broadwayman names derived e.g. Exorcist+Trebuchet=Xeiopelma;
Trebuchet/Tripper/Zombie with Quibbler/Quitter/Skeleton., as yet unnamed (unless you know better).
Trebuchet+Quibbler, Tripper+Quibbler, Zombie+Quibbler, Trebuchet+Quitter, Zombie+Quitter, Trebuchet+Skeleton, Tripper+Skeleton are also amphibious and also as yet unnamed (unless you know better).