Well, mercifully they don't bite. But they probably weight as much as a small child. He feels less hurt than he should've but that is likely the effect of the extra health he got from leveling up earlier.

He knocks that one off himself again.

… Can he tell what his health is while he picks himself up off the ground and continues to keep them away?

If he is looking for a health bar, he will be disappointed, he does get a sense of being "more than 100%" health, just because there is more of it to go around.

How much more than 100%?

Probably above 185% if he had to put in numbers? Definitely above 175%.

No clear shelter for him to keep away from the bats?

Besides his tent there is nothing obviously in the category of shelter. There are some nooks and crannies where he could defend and blow away bats that can only come from a single direction. Also, it started raining. How joyful.

Nooks and crannies sound like a better idea than running around all night, so he finds a nicely defensible one of those to hide in.

The rain can go screw itself.

Well, there is this one between these threes and that rock, which should allow him to see bats coming from a mile away.

He also can see the weird fire things coming from a mile away, as they slowy converge in his direction.

They aren't any more affected the next time he tries swiping at them, he supposes?

Not even one bit.

"Have you considered not doing this?"

The bats and fire-ball things are so rude that they don't even respond.

At least most of the fire-ball things have stopped approaching. But one soldiers on, slowly.

Is there any clear pattern to the ones that have stopped? Can he try running this one into a tree, does it only move in straight lines, could he trap it –?

The ones that have stopped are... not coming to close from each other? They fire balls appear to keep a minimum distance and stop moving if that means breaking away from that minimum radius. There is no clear pattern to how it moves, but it can avoid obstacles by lack of any considerable momentum.

He was hoping it had buggy pathfinding and he could shut it in a box.

What if he goes in some water?

The water gets agitated and he sees a pirana-like fish jump at him, it's jaws almost biting his leg with a very cartoony "chomp" sound.

He jumps back from it rather quickly and looks around for high ground.

There are several hills around, also a small mountain towards the center of the island.

Towards one of the hills.

Mercifully there is a respite of the rain when he gets there (after dodging a couple of bats).

The fire-balls things follow him slowly, but appear to give up once he is far enough away.

Oh what a terrible shame.

Can he keep the bats away from him on the hill?

Yup, there are trees, rocks and other places to put his back against to to have a better defensible position.

Of course, the bats are still attacking through out the night.

Can he drive them off?

– How far is he from his tent, is the fire still going? Getting a torch could have been a good idea…

He can see the tent from up here with the fire still going (but diminished because of the light rain), it isn't that far off.