As we know, hydras are fairly repetitive in terms of their mechanics. At this point, we already have four of these bosses. Each new one inherits an additional head from the previous hydra, but in practice, the fight doesn’t really become more challenging with each added head

There’s a main hydra and the soul heads of the previous ones
We simply avoid the soul heads and kill the main hydra
That’s it

The fight feels almost identical every time and doesn’t introduce any real difficulty beyond learning the new attack of the current main hydra

One idea I had was to give the soul heads HP and a shield mechanic similar to the main hydra. This would require players to actively fight the soul heads, and only after defeating them would they be able to damage the main head

For example, in the case of Oblidra, players would need to defeat all three soul heads first. The soul heads could periodically block incoming damage, preventing players from focusing down a single one immediately and forcing target switching. Only after all soul heads are defeated the player would be able to attack Oblidra itself. I think Oblidra would still provide enough challenge during this phase through its void-based attacks

Another idea would be to diversify the attacks of the previous hydra soul heads

Druidra: its bite could apply poison, reducing the player’s healing. As a soul, it could also gain a vine attack that roots the player in place, similar to the plant used by the Gardener Caveling
Crydra: its bite could apply a slippery effect
Pyrdra: its bite could set the player on fire