Every four weeks, the Hydra Clan Boss changes seasons and you will a different initial set of Hydra Heads. Not only will the heads change but also the affinity and sometimes the base stats of the champions. This will require you to adapt your teams to meet the new requirements. Sometimes this allows you to drop champions that were previously essential if a head is not in the starting rotation but in other times it might force you to have a completely different set of champions.
There are currently Six Seasons of Hydra Clan Boss made up from the current Six Hydra Heads. We have created Season Specific Guides to help you deal with the different requirements that is presented to you.