A comparative adjective is used when we compare and contrast two different objects. The adjective is either connected with the suffix -er, or add the word more. From the given sentence above, the comparative adjective used is "more forceful". The comparison is between the mighty water spirit and any creature of land or sea.
They can investigate about the topic being persuaded about throughout multiple different sources, they can not act on a whim and be like hey that sounds cool lets do it.