The party should aim to try and destroy the Ambling Bellow as fast as possible to stop it from deploying more Cryptos.
Thundaga and Waterga are effective spells against multiple Cryptos, as they can halt their current action and they are weak against Lightning and Water. A Saboteur or two can be useful as Cryptos is vulnerable to most statuses and the Saboteur's Dispel can null their buffs.
As a noun, the word cryptos means "one who secretly supports a certain belief or group." As an adjective, cryptos simply means "secret." This suggests the cryptos were automata hidden from the population of Pulse in Taejin's Tower.