Bring units with abilities that can raise SPR and who can cover against magic attacks, kupo!
Kefka also has attacks that inflict status ailments and stop, as well as attacks with an instant KO effect, so you'll want to bring along equipment or have abilities on hand that can nullify those attacks, kupo!
Kefka will use heartless angel to greatly reduce the HP of the entire party, so make sure you have a way to heal yourself instantly, kupo!
Statue of the Gods (Tier 3) is part of 4 phase battle in the FFVI Kefka Series Boss Battle