I used the basic production cost from the Corebook,but don't know if i'm missing something or the final weapon is too cheap.
For the slow effect i used the minimum caster level required for the spell, which is far lower than the caster level needed for all the other properties.
masterwork flail 308 gp
+3 enchantment 18000 gp
flaming property +2000 gp
frost property +2000 gp
corrosive property +2000 gp
slow spell on target after each succesfull hit (will DC14) 30000 gp
enchantment cost 54308 x 1,5 (for many different properties)
total production cost 81500 gp
Flaming, frost, corrosive are all +1 properties, so this will make it a +6 weapon together with the +3 enhancement, at 72000 gp. I don't know how the slow stacks with that.
Also, I'd suggest making your own enhancement called 'elemental fury' or whatnot, giving it 1 point of each fire, frost and acid damage on a successful hit. This would be a +1 or +2 enhancement depending on how kind you are to your players.
My problem was just this:the weapon from Baldur's Gate 2 only inlicted 1 point of each energy type, and i couldn't find anything like that.
Another solution would be to give it 1d6 elemental damage with 1/3 chance to do fire, 1/3 frost and 1/3 acid, and have that at +1. Roll a d6: 1-2 fire, 3-4 frost, 5-6 acid. To simulate the randomness of which flail head hits. (FoA has three flail heads each doing its own thing.)
As I recall, back in 3/3.5 there were a lot of different materials, metals from elemental planes etc. That would confer a single point of energy bonus damage to any weapon constructed of them. You could look these up, if you have the resources, and perhaps add their costs into the item, along with some fee for 'alloying' them together.
Otherwise, one point of damage from three elements is still only +3 which is the average damage effect for any one full-powered elemental property. I don't think having that be its own +1 equivalent power is too far out there.
The game the weapon was in used AD&D 2nd ed. rules.
I should have some books of that ed. so will look.It could also inflict 1/6 of a die of damage (so basically just 1 damage) for each one of the three energies, plus the slow effect.
Something like "every hit inflicts 1 fire damage,1 cold damage and 1 acid damage" so the property could cost 1/6 of the sum of the cost of the other three properties.
Assuming that 1 fire, 1 cold and 1 acid added up to a +1 bonus (not unreasonable considering how many things are resistant to at least one of those, so it'd compare well to 3.5 average damage of one type), you'd get:
- MW flail, 308 gp
- +4 total enchant, 32000 gp
- slow effect, 45000 gp (see below)
total - 77,308 gp
The big deal is the slow effect. 45000 is assuming it's use-activated, CL 5, and takes the *1.5 for different abilities. (You don't multiply the whole cost by 1.5.) It'd last 5 rounds and would have a DC of 14.
I'd suggest working out a slowing property though. It seems to fit better for on-hit abilities on weapons in most cases. I think it'd probably be a +2 depending on the details, which would make the total 72,308 gp (pretty small difference in this case).