how to allow multiple enhancement on a single weapon or armor without cousing serious balence issues. I figured using cost, weapon lvl and other such things as a way to balence it all out.
(as a side note some current magical gear levels slightly unbalenced but will make a difrent thread for that)
So for examples we can use (or any other enchantments)
LV 5 Flaming +1 longsword and LV 2 mages weapon +1 (just randomly selected enhancements)
for higher lvl example will use
LV 15 Fey strike longsword +3 & LV 14 shapechanger's sorrow +3
How could we add these enhancement into a single weapon and still maintain balence over all. could cost be a balence? would the combination change the weapons lvl? how would that effect the + of the weapon if the lv passed the usual set area where the + changes?
I like the idea of allowing my players to stack enhancements much like 3.5 allowed but I don't wish to couse serious balence issues from doing it.
* Pick two enhancements (any more and it breaks down completely)
* Both enhancement must be valid for the type of item you selected
* If the item has a Property, At-will or Encounter power, then that power must grow with the enhancement bonus of the item. (Some exceptions allowed; such as a property that simply toggles the damage type, but only if the DM says "yes")
* Pick a valid level for each of the enhancements
* Add up the levels for both items, this determines the enhancement bonus as well as the item's price.
* To determine properties and powers, build the properties as they would be for the enhancement at the level you selected
* To determine crit dice, add up the crit dice from both enhancements at the selected level.
Quick example:
The Sword of Fire and Ice combines the powers of the lvl 5 Flaming Weapon and the lvl 8 Frost Weapon.
First step, add up the levels. This weapon will be a lvl 13 weapon. Both apply to any weapon, so there is no limitation to the weapon choice.
Determine the enhancement bonus: a lvl 13 weapon has a +3 bonus.
Determine crit dice: the lvl 5 Flaming Weapon deals +1d6 fire damage, the lvl 8 Frost weapon deals +2d6 cold damage, so a Crit from the Sword of Fire and Ice deals +1d6 fire and +2d6 cold damage.
Determine properties: the weapon has the properties of both weapons. Dailies don't need to scale with enhancement and the at-will powers are exempt from the rule.
You could use both of the daily powers on the weapon, but each requires a Daily Item usage.
This system generates weapons and armor that are mostly balanced, but the DM should still consider each item seperately to make sure it isn't broken. Munchkins will tear this down and abuse it.
Any item more complex then what this system generates should be an artefact or plot item.
Every basic magic weapon has a certain level, just for the "plus".
+1 = Level 1
+2 = Level 6
+3 = Level 11
...
+6 = Level 26
Every enchantment, then, has a "level cost" that adds onto that. So, to use the examples above:
Flaming adds 4 levels, Mage's Weapon adds 1 level. Fey strike adds 4 levels, and Shapechanger's sorrow adds 3 levels.
It seems to me that combining all of these factors together, wouldn't be a terrible approach (with the obvious rule that the minimum enchantment bonus for a particular enchantment has to be maintained). Therefore, in the example of a Flaming Mage's Weapon +1, this would be a level 6 item - and would only have a +1 to hit (unlike other level 6+ items). The cost jump of going from the Level 5 Flaming Weapon to the Level 6 Custom Item would be 800 gp, which is more than a +1 mage's weapon costs in the first place (normally 520 for a +1 mage's weapon) - more than 50% more. Of course, that is because that particular combination of enchantments pushes the level of the item across the 5-level bracket and into the next one. Adding two level 2 weapons together to make a level 3 item wouldn't have the same effect - in that case, the cost for adding the second enchantment would be slightly less than the cost of a weapon with the second enchantment on it. But, hey, that's a crappy weapon, so a little discount might be in order.
Using our other example, combining a fey strike weapon (25,000) and a shapechanger's sorrow weapon (21,000) into a FS/SS weapon +3 would be a level 18 item (85,000).
As you can see, this approach would generally result in enchantments that cost a good deal more than either of the components, which makes them limiting both because of the large GP cost, and the level increase (so they generally cannot be made until you could have a weapon with a higher enchantment value). Off the top of my head, this seems sufficiently limiting - but, as I said, I haven't playtested this at all.
Based on the math (and how magic item prices go up faster every 5 levels), as long as the total level increase from enchantments is +5 or higher, it is generally (sufficiently) expensive that there is an obvious disadvantage. If the enchantments add up to less than +5 levels, you're really only paying for the individual enchanments - and it will typically be cheaper to combine them all together than to buy them individually.
I might suggest an additional rule that says that if the enchantments add up to less than a 5 level increase, you just add the costs of the individual weapons together, or even treat it as if the new custom weapon had an enchantment cost of +5 levels. Either of those solutions would make it less desirable to add a +1 level enchantment onto another +1 level enchantment weapon. I think there is already sufficent reason not to combine the "good" enchantments (due mostly to resulting item level/cost).
Just some ideas - your mileage may vary.
The Sword of Fire and Ice combines the powers of the lvl 5 Flaming Weapon and the lvl 8 Frost Weapon. First step, add up the levels. This weapon will be a lvl 13 weapon.
I like these ideas too - but would point out that if you take the level 13 weapon and say "oh, that should have +3 to hit since its between 11-15" that the cost of the enchantment is really only 2 levels more than a basic +3 weapon. One of the components (a flaming weapon) adds 4 levels.
Look at the sword of fire and ice (level 13?), and then look at a +3 flaming sword (level 15). Which would you buy?
I'd advise reserving these kind of weapons for things the players run across, not things they can make themselves, or at least limit them in how many they can make.
Yeah, they'll be more powerful, but not gamebreakingly so. You shouldn't allow players to combine anything they want, that's simply not going to work under 4e, period. This at least gives DMs or players the options to make some special weapons with multiple powers without breaking anything 
1: determine the 'base level' of the item by enhancement bonus
2: add a magic ability, add on the additional levels required by that ability (for example, if the ability is available as level 2, 7, 12... you would add +1 level, if the ability is available as level 4, 9, 14... then that would be +3 levels). You may only add the ability if the enhancement bonus of your weapon is high enough. If you have a base level of 6 (+2) but the ability is only available for +3 or higher weapons, you cannot choose the ability.
3: Add one additional magic ability as above, including enhancement bonus requirements and increasing the level. The final level is the total level of the item.
Example: A +3 weapon with a +3 level ability and a +4 level ability has a base level of 11 and a total level of 18.
4: The weapon enhancement bonus does not change when you add abilities, even if the level increases.
Example: For the weapon in the example above, the weapon would only have a +3 enhancement modifier, even though most level 18 weapons get +4.
5: You gain the properties and powers of both magic abilities. When you score a critical hit, choose the critical hit property from one ability. If the weapon has multiple daily powers each can be used separately and each consumes a usage of an item daily power as normal.
6: If a power or property for a magical ability depends on level, use the base level plus the level increase from that ability.
Example: Your weapon has base level 11, a +3 level ability and a +4 level ability. The +3 level ability has a power that adds 10 ongoing damage at level 14, and 15 ongoing at levels 19, 24, 29. Even though your total weapon level is 18, you gain the benefit of the level 14 version because a +3 weapon with a +3 level ability is level 14.
7: If a power or property uses the numeric value of the weapon's level in a calculation, use the full level.
Example: If the +4 ability from the weapon in the example above made an attack that was "weapon level vs ref", you would make a +18 attack vs reflex.
It's complex, but really rather balanced and intuitive. It shouldn't be too hard to run during sessions. If your players are sophisticated enough to want multiple abilities per weapon, they should be able to handle this no problem.
Personaly I like adding the lvl of the 2 enhancements together then using the cost and crit effect of a item of the combined lvl.
so a lvl 5 enchant and a lvl 3 enchant would use the Magical modifier, crit modifier and cost of a lvl 8 item. It was brought up to me earlier that this would allow some enchantments to be purcased for cheaper (in the case of a flaming weapon) however since a +2 weapon is no difrent from a +1 for these enhancements it makes no sence to me to have a +2 varrient cost so much.
OK so basicaly here is a better worded version of my idea
take all the enchantments and remove the +X modifier, and the cost.
Remove all powers that are now exactly the same, so a lvl 5 flaming and a lvl 10 flaming the lvl 10 flaming gets removed since s is absalutaly no better then the lvl 5 version.
This should leave you with a list of enchantments of varing lvls that all do difrent things.
So for the example of flaming there would be a lvl 5 flaming and a lvl 15 flaming
ok so now here is where the problem arrises, a lvl 30 power is much better then 2 lvl 15 enhancements and a lvl 20 enhancement would not even be able to be added,so instead of adding the enhancements lvl to determain the new lvl I purpose adding the enhancement costs then round up to determain the new iteams lvl
so adding a lvl 15 flaming and a lvl 15 lifebane enchants, both cost 25K so totle would cost 50K the new weapon would then be lvl 17
basicaly it would look like this
(useing longsword as a base weapon)
+4 Flaming longsword of lifebane LV 17
The enchantnt effects would be the ones listed at lvl 15 for both enchantments
The weapons crit would be as per the better of both enchantments
the weapons cost would be = to lvl 17 enchantment
This would keap the weapon prety balenced,
to those who managed to follow my ramblings (perhaps to those who can reword it even) what are your thoughts