User blog comment:Ghido/What monsters would team up?/@comment-31601543-20140225012134

Mothra and King Caesar, Titanosaurus and King Ghidorah, Hedorah and Destoroyah, Godzilla and Gamera, Ultraman and Jet Jaguar, Ultraman and Zone Fighter, Zone Fighter and Jet Jaguar, Jet Jaguar and Gipsy Danger, Mecha-Godzilla and Kiryu, Gigan and MechaGodzilla.

Added bonus: Battra and non kaiju Belivera.