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Human - Never a bad choice for a shaman. The hardest thing usually is landing your communes. You don't have the equivalent of spellcraft, so people with even cursory gearing for svs will often be very hard to land things on and the level advantage you get with a human helps all the way up. Doesn't help as much at hero. No vulns, decent stats. 4 pracs/level.
Arial - Dex doesn't help at all, especially as the greater carry # is sort of moot because shamans don't need much in the way of preps. Greater int doesn't give you much more in the way of mana, you will *never* have decent mana gains with a shaman. Perma fly is nice, as fly is the single most important prep with a shaman, but as there is a summonable mob to buy fly potions from, and numerous places to buy them, perma fly doesn't help as much as it might, as long as you are careful otherwise. I've never died to a thief as a non arial shaman though, unless it was a gang.
Storm/Firegiant - Horrible gains anyway you slice it, but thats more or less true with any shaman. Fire's get mildly decent hp gains. Possibly the best at hero because of resist phys. Storm especially can be nasty. However, on the way up it will be a pain because you will rarely have level advantage and landing communes will be a huge pain. Lack of int sucks in re: you have a lot of stuff to practice as a shaman.
Duergar - Some people claim this is the best race because as a shaman the two things you fear the most are thieves and assassins (cheapshot and assassinate). I would tend to agree, however you will have mana as bad as a giant's, and the str/con once again doesn't help all that much. For more information on how to play a duergar shaman search for Drucyrus logs. It should be noted however, as Daurwyn has said, its much harder than Druc made it look. Lack of int sucks in re: you have a lot of stuff to practice as a shaman.
Drow - No real experience here beyond ranking one to the high teens. Perma sneak will be nice with rot/wither, and my mana gains seemed decent with the 24 int. Normal problems all drow have (mithril vuln/little hp).
Dwarf - Only shamans with decent amounts of hp (usually about 114-15/level). However, IMHO if you are going goodie storm giants are better with resist phys, no vulns and their other advantages.
Halfie - People revile halfies all the time, however you will get 5 pracs/level, none of your stats suck, and quiet movement is never a bad thing. Minor vuln isn't a big deal with sanc/prot. IMHO probably on a similar level as humans, plus you get the niftiness in terms of roleplay of a halfie.
If you aren't ranking on overly tough mobs for your rank you can tank reasonably well. Obviously a real tank is better, but with sanc, prot, cure crit, a sword and a shield it is doable, especially as a giant. I've done it from about 24-35 with a human shaman and it was fine.
You don't have all that much to do when ranking so it helps if you can lead the group. Also, rank when ever you can. Shamans just get better with ranks up until 40, so rank sitting is never a great idea, unless you are human and want to sit around 30 and clean out your range, which you can do but does get boring because its so fucking easy.
Gear for mana and hp's equally. People will yell at me because of this but its true. With sanc/prot/cure crit you will stay alive pretty well, but sanc/protective shield is difficult to keep up all the time from 24-40, unless you have blackchannels (or spiritual link). You can't pk/survive without mana, so gear for it. Great gear for a mid ranks shaman are things like pitchblack rings and topaz bracelets, i.e things that help both hp and mana. However, if its a choice between an equal amount of hp and mana, and you already have enough hp to feel comfortable, take the mana, as it is convertible into cure crit, and total equals more overall hp this way.
Once you have enough hp/mana to feel comfortable gear for -svs.
Never gear for damage. If you do you are a tool.
ALWAYS HAVE FLIGHT POTIONS.
Stone skin and shield are useful but not overly necessary. Stone skin is good if you want to charge groups of three, but you can still do it with out, if the group isn't badass, pre hero. At hero stone skin is easy enough that you should have it up a lot of the time. Trannies and slow items are your friend to assist with mana regen.
ALWAYS HAVE FLIGHT POTIONS.
(updated by Yhorian)
Afflict is cool. At high ranks, some of the maledictions are pimp. One stops them from scanning I believe, one is -10/-10 hit/dam and prevents resting. Can also cause bleeding, and is physical damage.
Refresh is nice at low ranks, for obvious reasons especially since the happy boots aren't happy any more.
Blindness is sooo nice at low ranks. Vs. many foes this will be the real thing which seals the fight at low ranks, especially when combined with summon and plague. Always get it off if you can, because if the fight does go against you it will allow you to get away, and if the fight does go your way, blindness makes it much easier to to seal the kill.
Protection/sanc/protective shield. Keep these up at all times. (Haven can now replace Sanc as a permanent protection, and gives about 25% dam redux if you're surprised. Sanc can be put ontop to cancel it out if you spot a foe coming)
Earthquake is useful for getting thieves out of hiding sometimes. Also, if you are blinded for somereason (dirt kick etc) and you think your foe is in the room with you, earthquake will start combat for you.
Poison. Very nice at low ranks, decent -str, very nice vs cloud giants. At low ranks I have found that a decent chunk of the time this is enough to make them drop their main wield. I recommend laying this down before weakness against fighting classes as it messes up their regen as well as hurting their str.
Weakness. Obvious uses, lay down after poison unless you are sure that the greater str loss from weakness will make them drop their main wield.
Summon is well, summon, and other people have written much better things than I can about it. One note, however. Unless you have a whole lot of mana from gear, don't use it that much pre about 20. it won't work very often and will burn through your precious mana. At mid ranks, this will let you and one more person tear through almost and group of three.
Famish. I always skip it, but some decent shaman players have said its decent. *shrug* try it out and prove that it doesnt suck if you want, however, I'd always rather land a blindness, weakness, poison or plague. If you've landed all that, than you might as well be harm/fatigue/demonfireing. (blind + famish is great versus disease resistant warriors, some people won't register they've just had the equivalent of plague thrown onto them)
Dispel good/evil. Practice the one that is of your same align. I.E if you are evil, practice dispel evil. It it will be rarely useful against people of the same align. Also, if you are evil say, dispel good can be used when ranking as a damage spell that doesn't suck up your mana.
Mend wounds. Know it, love it. heals 55 hp or so at high ranks. If the fight is going against you, but you still have mana left, FLEE (don't heal in combat!!!) and mend wounds a few times and then return and kill them.
Curse. Obviously good against people you think will recall. More useful for the fact that it lowers their svs and lets you land more communes. Harder to land than Damnation though.
Plague. Obviously a nice thing. If you are using it vs. warriors for the str loss, use weakness/poison first. Against communers/spellcasters the main use is to get rid of their mana. Also, very nice against ragers to get rid of their moves. Get plague off, and then flee a bit until they are out of moves. A rager that can't move is eventually a dead rager.
Tsunami. I am sure a player like nep or daurwyn can figure out some amazing use for this commune. If you aren't like them, skip it.
Unveiling. Obvious uses. Earthquake is often a better choice though.
Dispel. Know it, love it, consider perfecting it. Dispels communes and spells. Always use this against classes that have sanc. Vs. paladins/shamans it will be your fight winner, along with energy drain/ plague. So disgustingly nice. Read Drucyrus logs for full implications of this commune.
Energy drain. Underused with shamans. Nice against communers/mages to get rid of their mana. Also very ncie vs. ragers to get rid of their moves. Nice against anyone that doesn't have teleport potions and is allready cursed/damned so they stay in one freaking place. This combined with plague will make almost anyone stationary. Use it, love it.
Damnation. Prevents recall just like curse. Seems easier to land than curse is. Random maledict affect. You can really mess people up this way (use the Voice of Condemnation edge to get stackable damnations). If you just want to prevent recall, this is probably better than curse.
Fatigue. Mental damage, and nice mental damage at that. Also can sap some moves from them (if they fail their save). Good commune.
Turn undead. Goodie only, for ranking/vs. necros.
Redemption. Gets rid of damnation. (low success rate, high mana usage)
Demonfire. Triple star damage vs. unprotected targets. Your bread and butter damage commune once you get it, however vs. fire giants fatigue is better, and vs. duergar dispel evil is better.
Rot and wither. Are well, rot and wither.
Aristae. Never really used it, perhaps someone can recommended ways to use it. (gives +300 hp, a haste-like effect, +dam, +hit and prevents you escaping combat through most means like flee and word)
And thats Larcats half brained shaman faq.