The Tavern

The only brand from the resistance tables that does not spawn as weapon ego. Could be fun!

http://crawl.chaosforge.org/Punk

I think the reason there aren’t more is because corrosion against monsters is REALLY strong (remember acid wand charges are some of the rarest too).

If Corrosion is REALLY strong, we can make it exceedingly rare to compensate... how about 0.3% on a scroll of brand weapon?

How about 0.0%, that seems to be working fine

It's the same mechanic as electrocution (extra flat damage), just more powerful. That wouldn't be interesting to add to the ego pool. It can get away with being on an unrandart because the standards are lower for unrandart-exclusive brands - no way thermic engine's flame+freeze will ever become a random ego, and disruption and dragon slaying were removed as random egos ages ago.

Then get rid of it. Spider Nest is hard enough as is. As is Hell.

I think you are misunderstanding why Punk is good. The corrosion status itself against monsters is really not that good; all it does is take away 8 AC. Most monsters don't even have a full 8 AC to take away. It doesn't reduce their accuracy or damage or anything.
However, what Punk and wands of acid do is "splash the monster with acid", which deals 2d4 extra, AC-ignoring damage, and incidentally applies the Corr status 2/3rds of the time. Applying the status happens after the sling bullet/acid beam's damage has already been dealt, so the AC reduction doesn't even do anything until the next time you hit the monster. It is the extra 2d4 damage, not the corrosion, that makes Punk so good. That's a mean of +5 damage per hit. Electrocution does a mean of +4.67 damage per hit. It turns out that electrocution is very good, so a slightly better version of electrocution is also very good. The corrosion is just a little bonus against monsters with AC.

Entropic weave applies the Corr status directly, it doesn't do any damage at all. The player Corr status is also different from the monster Corr status, since it reduces accuracy/damage and has more than one possible level. It is also trivial to deal with by running away and waiting for it to expire.

Does electrocution ignore AC too?

Yes. Depending on how you look at it brands all "ignore AC" in that the damage is just rolled then directly applied after resistance, however percentage based brands like fire and freezing have their damage based on the weapon damage done after AC is applied, so their damage is effectively reduced by AC in advance (if you applied AC to fire/frost etc percentage type brands you'd technically be applying it twice)

Thanks.

Based on the wiki, there are very few acid resistance monsters outside of Slime. Electricity resistance seems to be a good deal more common.

Also, a guaranteed 5 damage every hit is more valuable than 14 damage 1 out of three hits.

Furthermore, I think duvessa underestimates how good it is to reduce monsters to 0 AC.

Corrosion on monsters doesn't stack unless I'm mistaken, it's just -8AC while they're corroded. Which isn't bad, but there really are a lot of monsters who don't have much AC, even late in the game.

duvessa's point:

bears remembering and expanding upon: usually, player and monster status effects are totally different things, even if they have the same names and methods of application.

Yeah, acid resistance effectively does not exist on monsters.

Thanks for the explanations all. Since many code changes are defended by saying things are made easier to understand and more unified it seems not nearly all of the games mechanics are anywhere near that goal.