This HTML document is hereby placed in the public domain. It is intended to be used with version 3.4.3 of Nethack.
For the purposes of this spoiler, "naked AC" refers to the armor class that your character possesses when he/she is carrying no items, is not polymorphed, and is not under the influence of any protection spell. Intrinsic protection is defined to be the amount by which your character's naked AC is less than 10. Intrinsic protection is usually zero or positive, but it can be negative in the unlikely event that you have eaten a negatively enchanted ring of protection (see below).
In Nethack, a character is considered "protected" if he or she has undergone any discrete event that increases his/her intrinsic protection, even if the amount of the increase happens to be zero or negative as a result of eating a poorly enchanted ring of protection. Being protected affects how much protection you can gain by donating or praying (see below). You can find out whether you are protected by using a wand or potion of enlightenment during your game, or by ending your game and reading the messages that are displayed when your game ends.
Here are all the ways to gain intrinsic protection and become protected:
The following events will cause your intrinsic protection to be set to zero.
Unless your protection was stolen by a gremlin, you will still be considered protected after any of these events occur, provided that you were protected before.
David Jao <firstname.lastname@example.org>
by Doug Freyburger 02 Mar 2006
For divine protection you want 1d(luck+6)/2 = 6 at the time you pray. Characters start their games with luck=0 on most days, and on full/new moon days it settles back to 0 by turn 600. Before reaching the altar in minetown a character generally knows his/her luck is 0.
The problem with raising your luck via four-leaf clovers is that you need to look up the monster in the table in the prayer spoiler to tell how many luck points you gained. So it's easier to max out your luck at 13 and then move back down to a known number. Below is my commentary on each luck value from 13 down, based on first maxing out your luck and then deliberately moving it to a known value before praying.
Given the various treats it makes sense to pick up all available cursed items that you want uncursed, in case the light blue glow happens. It also makes sense to wield any damaged weapon in case the fix-weapon treat happens and lacking any damaged weapon an uncursed one, especially any stack of uncursed missiles like daggers. Over time you'll run out of damaged weapons and slowly build more blessed ones.
Without holding a luckstone, luck maxes at 10 and it would take 2 mirrors to drop your luck down to 6. But without a luckstone your luck drops by 1 every 600 moves, so it would be hard to keep track of your luck.
While holding a blessed or uncursed luckstone, luck maxes at 13 and it would take 4 mirrors to get down to 5-6 for the prayer effect a combat wombat wants, or alternatively 3 mirrors for the spell caster (who wants books as much as AC protection) to get down to 7-8. At this point you could keep the stone in the open, max your luck, break 3 or 4 mirrors, and know you'll never get crowned if you pray every time you reconcile. That could go on until a "create monster" spell no longer makes any monsters on your level if you're a wizard who does not get hungry from casting that spell. My conclusion is that any spell caster who gets "create monster" to 0% failure can use prayer to get an excellent AC with a bit of altar work.
Breaking 3 or 4 mirrors while holding a luckstone has the advantage that it takes you 1 point lower than you need but it still gives the same prayer result when compared to killing coaligned unicorns. On the other hand killing coaligned unicorns may be a goal anyway for an extinctionist player.