I thought mithril gear only ignored acid. Has it traditionally ignored fire as well?

It is metal. Anything metal should ignore fire, as no other metallic gears burn except apparently gauntlets and boots. Bodyarmor, shields and helmets made from metal ignore fire I think (can't remember for sure just now and too tired to check).

It seems that shimmering critters interfere with the new targeting indicators. And they make hallucination *seriously* disturbing, but that's not necessarily as much of an issue.

Is there some way to make the screen just refresh those critters, rather than redrawing the entire screen each animation frame?

I believe that this is the reason for flickering overhead term window. Each time flickering monster changes color, entire overhead screen gets redrawn.

Suggestion
- When turning off the option "Color: shimmer multi-colored things"
- Show the thing in it's original color only, otherwise it's easy to confuse it with something else.

- No matter if the option is on/off, show it in original color on the overhead map. Would remove the need to redraw the overhead map, and would help with the problem that Timo (and I) have with the overhead map flickering and slowing down the game. If the option is on, the overhead map flickers every time the monsters switch color, if the option is off it's the same, i.e. the overhead map flickers every turn, so running is slow, and resting more so.

I checked. The only base items with IGNORE_FIRE are

Mithril arrows and bolts (but not mithril shots)
Ethereal cloaks and slippers
Alchemist's gloves

So the inconsistency is that mithril arrows and bolts ought to lose it.

I would say that metal items should be immune or at the very least much less likely to be damaged by fire.

Also I've never understood why equipment you are wearing get merely damaged by elements, but when they are on the floor they get destroyed in one hit. It should be affected in the same way regardless of whether it is worn or not.

This would be a very big change, making fire damage much much less of an issue. That's not to say it shouldn't happen, of course.This is a fair point - but this is only one of a large number of inconsistencies between the treatment of the same object in different places (floor, worn, your pack, monster inventory).

Of course, most metal items are weapons or hard armours, which are unaffected by fire by default...

I'm not talking about flag, base item types shots and bolts, swords, hard armor, dragon armor, shields and helmets/crowns do not burn. Which includes a bit oddity, because from those there are "hard leather cap" and "leather shield" which are leather and "wicker shield" which is wooden, which all should burn quite nicely. OTOH, all of the rest of the items in those groups are metallic (except rounded pebble which is stone), which I guess is the reason they have been giving immunity to fire. (though I'm not sure about dragon armors because they seem to all have ignore_all flags).

Anything Mithril definitely should be immune to fire for consistency reasons. Mithril bolts can lose the ignore fire-flag, they are not vulnerable to fire anyway.