I've blogged about the most potent first level spell in the game already, but I want to take a look at making it even more powerful.
Shillelagh is the exact same spell both in D&D 3.5 and in Pathfinder. The central idea is that a club or staff gains a +1 enhancement bonus and (best of all) does damage as if two sizes larger.
As the PF version specifies, a small size club or staff which normally does 1d4 now does 1d8. A medium size club hops from 1d6 damage to 2d6. That puts your lowly club on par with a greatsword, and you do not even need two hands to use it.
This is all old ground, covered before. Now let's see how much spin we can put on this fastball to jazz it up.
Size. You may be tempted to try to cast your Shillelagh on a greatclub. Stop right there. The spell only works on clubs and staves, as stated. Trying to extend that to greatclubs is clearly a stretch -- a stretch too far. ... However, the rules do say that you can use oversize weapons ...
Inappropriately Sized Weapons: A creature can't make optimum use of a weapon that isn't properly sized for it. A cumulative –2 penalty applies on attack rolls for each size category of difference between the size of its intended wielder and the size of its actual wielder. So even though you cannot cast Shillelach on a greatclub, you can get a club one size too big for you, wield it with two hands, take a -2 attack penalty, and cast Shillelagh on it! If you are medium, you can use a large club that has a base damage of 1d8, and after casting Shillelagh on it, the base damage zooms to 3d6!
Moar Size. Sure, using an oversize weapon is fine, but how can you make it even bigger? With Enlarge Person, you and your gear increases a size category. An enlarged human carrying a large size club (using two hands to wield it) becomes a large size biped (thus with a 10 ft reach, sweet!) with a huge size weapon. That's a base 2d6 damage before the Shillelagh is cast, rising to 4d6 with the first level spell. Note that 4d6 is your cap, because Shillelagh takes the huge damage, boosts it two sizes to colossal, and there is no result larger than colossal.
Speed. Now, yes, the combination of Shillelagh and Enlarge Person is pretty sweet, but it takes you two rounds of casting to be ready to attack. That's two rounds of combat you just missed. So what can you do about that? Well, at low levels, there is only one possible solution I have found. If you're playing the Pathfinder flavor of D&D, and if your DM is allowing the use of subdomains in the Advanced Players Guide, then you can request the Growth subdomain of the Plant domain for your druid domain. Look at the special ability you get at level 1:
Enlarge (Su): As a swift action you can enlarge yourself for 1 round, as if you were the target of the enlarge person spell. You can use this ability a number of times per day equal to 3 + your Wisdom modifier.
Holy crap! Casting as a swift action is the same as casting a quickened spell, and even with a duration of only one round, this is amazing! In the first round of combat, you cast your Shillelagh and move up to your foe. In the second round, you enlarge as a swift action and attack! You've cut your prep time in half.
(By the way, if your build includes levels in barbarian (and that's a very strong option), then note that you can use supernatural abilities ("SU") even while raging, even though you cannot use spells or spell-like abilities. So you can activate your Growth subdomain power even while raging!)
Still, that only gives you 3+Wis rounds per day. You may need more, even many more rounds per day. Well, by mid-level, you should be able to gain an unending supply of enlarged rounds, if you are willing to accept drastic measures -- in just two words: Permanent Enlarge!
Per the D&D 3.5 equipment list and the Core Pathfinder version of the same, in a large city you should be able to hire a wizard to cast fifth and sixth level spells for you at very reasonable rates. A first level spell, like Enlarge person, cast by a 10th level wizard or sorcerer, costs 1 x 10 x 10, or 100 gp. A 5th level spell, like Permanency, costs 5 x 10 x 10 = 500 gp, cast by the same 10th level arcanist. You have to pay for the material component, so a Permanency cast to make an Enlarge Person spell last forever costs an extra 2,500 gp, for a total of 3,100 gp. Following the standard wealth by level table, you should be able to pay for that by 4th or 5th level. And if you are permanently large, you do not have to take the time to cast Enlarge Person, so all you have to do is cast Shillelagh at the start of the battle and you are set.
(Caveat Minimaxer: Being permanently Enlarged has its plusses and minuses. The +2 Str -2 Dex size adjustment is probably good for a club fighter. The 10 ft reach is unremittingly excellent. But there are major downsizes, such as fitting into carts and taverns, using the squeezing rules, and simply being taken as a giant or ogre and attacked on sight. You might want to consider a dwarf character, because an enlarged dwarf can stand as low as 7.5 feet, while an enlarged human can go to 12 ft-plus. Make sure your DM is on board with your plan before you execute it, or be willing to face hordes of villagers with pitchforks, many mazes of twisty little passages, all alike, and magic armor that never fits people your size.)
Speaking of Permanency, you may be able to get the Permanency spell cast on your Shillelagh, too. The spell does say, "the GM may allow other spells to be made permanent." Still, were I the DM, I would likely not allow it as unbalancing ... or I would price it as equivalent to a +3 or +4 weapon. Another option might be a long-duration advanced Shillelagh, by analogy, like Greater Magic Weapon is to Magic Weapon. Maybe something like this homebrew one ... if your DM is very kind.
Moar Speed. Now, casting Shillelagh still delays you a round from jumping into battle. Your ideal is to cast the spell quick-like. The Quicken Spell metamagic feat would work, if you have fifth level slots to use for the idea.
However, odds are that you are not a straight up druid. Likely you are multiclassed with some barbarian or ranger or fighter levels (or two or even all three). So that 5th level druid spell and the Quicken Spell feat are out of reach. What you CAN reach for, with enough gold, is a lesser metamagic rod of quicken spell. That's a sweet 35 grand goodie you should totes be looking for at some point after passing 10th level. That way for at least the first three fights of the day, you'll be in there clubbing in the first round.
A Vital Feat. A main advantage to a high BAB (as opposed to having a relatively lower BAB and piling on bonuses from high stats and magic items) is that at higher levels you get iterative attacks. From BAB +0 to +5, you get one attack a round. But at +6 and better, you get "iterative" attacks, that is, extra attacks at lower chances to hit. This is all review for you jaded rules mongers out there.
But passing on to Pathfinder Only rules, there is an interesting new option: give up your iterative attacks in order to boost your single attack. The Vital Strike feat says:
When you use the attack action, you can make one attack at your highest base attack bonus that deals additional damage. Roll the weapon's damage dice for the attack twice and add the results together before adding bonuses from Strength, weapon abilities (such as flaming), precision based damage, and other damage bonuses. These extra weapon damage dice are not multiplied on a critical hit, but are added to the total. The key here is this: "When you use the attack action" ... that is, when you attack as a standard action, not as a full round action. So instead of a full round of iterative attacks, you get a single attack (at double base damage) and a move action.
NOW you begin to see the sweet sweet options! Your enlarged oversized shillelaghed club is now imposing 8d6 damage per hit instead of a measly 4d6. It's like every blow delivers your own personal fireball, with no save for half! You only get to swing once per round though, but that seems fair considering the damage you're dishing.
And you still have a move action to use each round. The Spring Attack feat springs to mind -- move, attack, and move again. That's especially sweet with your enlarged reach (which grants you more swings per round, with each AoO you take), so consider Combat Reflexes too, if your dex is not low.
So get out there, you strength-optimized, permanently enlarged, shillelagh-wielding dwarfish thing, you! It's clobbering time!
Updated 24 Nov 14 with the details on the Growth Domain special ability.