Dungeon Master
Posts: 625
Joined: Thursday, 23rd October 2014, 03:08
Some notes about spell success penalties
First, here's a summary of what this post covers: This is going to explain (roughly) how spell level, spell schools, spellcasting, Int, Str, ER, shield penalties, Armour skill, and Shields skill relate to each other regarding maintaining a specific spell failure %, specifically how many spell levels each type of penalty corresponds to. This does not explain how to estimate your % failure rates using these stats, you'll have to go back to wizmode for that.
Second, this is working off the formula as explained on http://crawl.chaosforge.org/Spell_Success, which may or may not be accurate to whatever version of crawl you're playing (but it should be accurate to 0.21, the latest stable version as of this post):
If you want the details to how I've derived these estimations, they're in the following spoiler:
Now for the actually interesting part, the summary. When I say +X spell schools I mean increasing the average of all relevant spell schools by X; For example, if X is 1 and you have a dual-school spell this can be accomplished by training a total of two levels between the schools, either +2 in one school, +1 in both, +0.5 in one and +1.5 in the other, etc. As a reminder, a stepdown is applied to "spell skills" so these values are not correct (except for spellcasting) if you've already trained a lot of skills (and I mean +20 skills), they'll be higher.
- +4 spellcasting is equal to +1 spell schools.
- +6 Int is roughly equal to +1 spell schools.
- For spell levels, you need to (roughly) train additional spell schools according to this table:
To explain these tables: Let's say you're casting Confuse at 15% failure rate. Then if you train +3 hexes, Cause Fear will be at (around) 15% failure rate. Similarly, let's say you have Flame Tongue at 28% with 0 Spellcasting/Fire/Conj. Then Bolt of Fire will be castable at (roughly) 28% with 12.5 Fire/Conj. Also, as spell failure likes to hang around 1% a lot, the requirement might be lower if you're comparing to a spell that currently has 1% fail rate. - Armour skill modifies your ER penalties by a multiplier between 0.4 and 1, linear in your Armour skill. Some easy values to remember are 22.5 (0.5 modifier) and 11 (approx 3/4 multiplier).
- For armour, if your Strength is equal to ER, then your penalty is (roughly) equivalent to +ER/2 spell schools (this value may be off by 1 depending on your exact armour), scaled between 0.4 and 1 based on your armour skill. So if you wear crystal plate armour with 23 Strength, you'll need to train (roughly) +11.5 spell schools to get the same success as in robes. If you had 11 Armour, you'd only need to train (roughly) +9 spell schools instead.
- If you want a bit more precision or don't have Str = ER yet, you can estimate your ER penalty by +ER*2/3*ER/(Str+3)). Obviously not as catchy.
- For shields, assuming you have 0 shields skill, Bucklers give a penalty (roughly) equal to +1.5 spell schools, Shields give a penalty (roughly) equal to +5 spell schools, and Large Shields give a penalty (roughly) equal to +8.5 spell schools. Shields skill have a multipler that's linear between 0 and 1, reaching 0 at a specific breakpoint value. The value depends on your species and shield so you'll have to look up the exact number; I'm not going to post them.
- For this message the author CanOfWorms has received thanks: 8
- duvessa, kurzedmetal, Nebukadnezar, Octopode-monk-of-XOM, Patashu, Shtopit, Torax, VeryAngryFelid