Floating character during stream

If you *want* it Lo-fi then I would be tempted by just using cycle layers in a loop E.g. set advance frame to once ever 0.5 seconds (not every frame), then make 8 copies of the same image, just sliding it up each picture. You can autoreverse the sequence too in cycle layers, which would make 16 frames. That would bob up and down forever every 8 seconds.

How long is a stream typically?

One old school idea - use cycle layers as you can loop it. Okay for short sequences.

New fangled idea. Use a replay with a trigger. Record lots of up/down movement. If a long stream, you may need to trigger to kick it off again, but you can record a few sequences and trigger different ones for a little bit of variation, when there is a pause in the main action.

I used replays hooked up to a midi keyboard for a stream. Just press some keys at times to keep it going - was not too bad. E.g. you can hook the angry expression midi key also up to a different fish sequence, so just using the main puppet nudges the fish along into different sequences as well.

You also have eye blink to introduce some variety (e.g. two cycle layers - a default one, and an autoblink triggered one).