This is an admittedly silly way to play [Hydroid], but it is still surprisingly effective and can even stand up to solo steel path survival missions if your weapons are strong enough.

We overwrite his 1 with Resonator and take the [Conductor] augment. This allows [Hydroid] to not only distract the AI but to also lead enemies around, directly into his pool or tentacle swarms. Most of your time, you'll be hanging out in pool form using your resonator in this way, maintaining total safety due to the boosted duration and efficiency stats.

When you feel you've collected enough unwitting mobs in your pool, simply charge cast his tentacles to surround your pool, then leap out of the pool. Any still living enemies collected will immediately ragdoll and get picked up by the tentacles, making them easy targets for your preferred AOE weapons. Use [Rolling Guard] to get a few extra seconds of blasty fun in, then drop back into your pool, rinse, and repeat.

Have fun playing dirty tricks on the AI, Tenno.