Hear me out:
- Most staves give +Resistance. The only staves that don’t are Conjuration and Earth.
- Conjurations is a very wide spell school, and its melee attacks are typeless & checks AC once.
- Earth is also typeless. Its melee dealing +33% damage (compared to Conj), but it checks AC thrice. Given that Earth school isn’t as big as Conj, I think there’s a clear disparity in power.
The most obvious “resistance” for earth would be +AC, qazlal already gives it. But with protection being changed a while back, I don’t think this is desired.
Therefore, I suggest +strength. Strength gives some form of defense - but it mostly gives it through your armour/shield, which you can’t really hotswap. It also makes melee a bit more viable. Like it can be +3 or +5 str or so, because str is more impactful if you have low-str.
Known ‘problems’:
- Lowering failure rate can encourage fiddly swapping (but so do artefacts, and magic staves in general. Staves aren’t that common)
- It may be unintuitive. IMO it’s on theme (think ‘strength of atlas’), but it’s not super obvious from the name “staff of earth”.
- It can be messy with randart staves. Any staff with Earth would be forced to have +3 str, meaning it can never be +9.