On Metamagic

At high levels (such as Glorious Few, the Epic Ravenloft game I seem to have gotten myself into) some of the metamagic feats could be stacked in a particularly devious and twisted way. The following are suggestions to referees who wish to curb this; things put as 'recommendations' should be considered DM rulings for my games, other things are not (yet).

Additive Metamagic and Motes

Some metamagic feats cause the entire effect of a spell to happen more than once. Twin Spell causes the effect to happen twice in one round, Repeat Spell causes it to happen again in the next, and so on. I recommend that Energy Admixture be treated as additive metamagic, equivalent to Twin Spell plus Energy Substitution/Energy Affinity (depending on which source you have it from).

Terminology

A mote is a magical effect as written up in the spell descriptions in the PHB and elsewhere. An additive metamagic feat creates an additional mote, with some condition (alongside the original, a round after the original, or with a particular energy type). Regardless of how you stack them, multiple additive metamagics only affect the original mote; this means that you will always get one additional mote from each additive feat. For example, a Twinned, Repeated spell makes three motes, one from the base spell, one alongside it from Twin Spell, and one the next round from Repeat Spell. Repeat Spell does not affect the Twin mote ('two doublings equals a tripling', remember).

Mote Metamagic

Mote metamagic affects only a single mote, even when additive metamagic has been used to get more than one mote out of a slot.

Example: a Maximised, Twinned spell has one normal mote and one maximised. An Enlarged, Twinned spell has one mote at normal range and another at double range.

Even feats that cannot normally be stacked can be added as many times as it takes to apply them to all of the motes spawned from that slot (i.e. once for each additive feat used), without buying the feat again. Taking the example above, most spells that one would Twin would then need Enlarging twice to be worth Enlarging at all.

Some metamagic affects the 'variable, numeric' properties of a spell. These tend to say how they interact: a Maximised, Empowered spell has the maximised normal effect, plus half of the effect rolled as normal, and Intensify Spell states that it does not stack with 'any other feat that affects the variable, numeric effects of a spell'. At the DM's option there may be some spells that deserve to be treated as having 'variable, numeric' effects for the purpose of Empower Spell and perhaps Intensify Spell (the new ability enhancement spells spring to mind, since they used to be variable, and I'm sure people can come up with others).

Note that the half-and-half metamagic feats (such as Sacred, Consecrate, Corrupt and Vile) stack by cutting each type of damage in two: a Corrupted fireball does half fire damage and half unholy damage, so a Violated, Corrupted fireball does one quarter fire damage, one quarter vile fire damage, one quarter unholy damage and one quarter vile unholy damage (an in case you were counting, it now has the [evil] descriptor at least twice...).

Slot Metamagic

Some metamagic feats affect the way the spell is cast, rather than the effect it has. These feats are applied only once, since a spell slot (and however many spells it spawns) is cast all at once. These feats include Quicken Spell, Silent Spell and Still Spell. Slightly different but also in this group is Heighten Spell (and Improved Heighten Spell); this should be considered the most fundamental metamagic feat, and is always applied first.

Improved Metamagic and Stacking 

Terminology

When metamagic is stacked with itself, each use of a metamagic feat is called a layer.

Some metamagic feats can be applied more than once. The Enhance Spell explains how it stacks; you may add it once for each time you have bought the feat, adding +4 to the level of the spell slot each time. As noted above, you can reapply spell metamagic once for each additional spell gained through additive metamagic; this stacking does not require additional purchases of the feats in question.

One of the most powerful feats in the game when stacked, Improved Metamagic reduces the level cost of every metamagic feat the caster knows by +1, to a minimum of +1. As a suggestion (watch my wording; not yet a recommendation), add the levels of multiple layers of a single metamagic feat before taking off the effect of Improved Metamagic. So to increase the damage cap of a damaging spell by 20 levels, buy Enhance Spell twice, use a spell slot +8 higher than normal, then take the number of purchases of Improved Metamagic you have from this +8.

Alternatively (and this one is in my games for playtesting, as an option for players who want to use it) allow stacking of feats that do not normally stack, without extra purchases, but with the above condition on Improved Metamagic. The feats that will stack under this option are (and I'm not saying all of these are worth it):

Chain, Consecrate, Corrupt, Delay, Empower, Energy Admixture, Enlarge, Extend, Intensify, Purify, Repeat (see below), Sacred, Split Ray, Twin, Violate, Widen

When stacking metamagic like this, you add together the cost of all the purchases of the same metamagic, then take away your Improved Metamagic discount. The minimum cost is +1 per layer of metamagic.

Example: if you want more than one extra mote at the same time, you could stack Twin Spell with itself. Twin Spell normally costs +4, so using it twice has a total modifier of +8. You take the number of purchases of Improved Metamagic away from this total rather than each layer, but you must still pay at least +1 per layer (even if you have 7 slots of Improved Metamagic) for a minimum of +2.

A doubly consecrated lightning bolt does one quarter doubly holy damage (although unless your DM says otherwise, this is equivalent to normal holy damage), two quarters (i.e. one half) holy damage and one quarter lightning damage. [I did warn you that some combinations would be less than useful.]

Think carefully about how things stack, and if in doubt use the percentage version that I have used on the table below rather than the multiplicative version in the book. For example, Empower twice would be +100% variable effect. [As it is described, Maximise works on 100% of the spell's normal effect, so two Maximise layers will maximise the extra from both Empower layers (but that is the same as Intensify and more expensive).] Obviously there is no use in maximising twice, so only the doubling aspect of the second or subsequent Intensify layers have an effect.

Crazy Repeating

For those of a slightly strange disposition, try this. Stacking Repeat Spell gives you an additional spell the in the second round (for a total of two in the second round). If you wish, for +2 rather than +3 the stacked Repeat can happen the round after; for a total of +5 levels you get the initial spell, then another for each of the next two rounds. Extra spells in the fourth and subsequent rounds are +1 level each; you cannot arrange a late repeat unless there is already a repeat in the round immediately before it.

Stacking, Step by Step

In case these clarfications have made things less than clear, there now follows a step by step guide to stacking metamagic.

Step 0: Choose a spell and a level

Obviously the first step in choosing a metamagic effect is to pick a base spell. In addition, you may well want to choose the number of levels you have available for metamagic at this stage; it is easier to keep your monstrosity under control if you work to a budget, so to speak. As for planning the effect, it is difficult to get the full potential out of more than one mote unless you have several slots of Improved Metamagic, and several spell levels available; that will be an important decision later.

Step 1: Slot Metamagic

Some metamagic feats affect the entire spell slot. These include the Heighten Spell feats, as well as Quicken, Still and Silent Spell. Slot metamagic feats are marked as such in the table below. Most slot metamagic feats (Still, Silent, and so on) are purchased once only.

Step 2: Additive Metamagic

The next step is working out how many effects you want. You can increase the overall effect of a spell by adding additional motes using additive metamagic (see that section, above). Each use of an additive feat gives you an additional mote, but each mote must be improved separately in the next step, so it may be possible to have too many to use effectively. Additive feats are marked in the table below by having 'Add' in their type column.

Step 3: Mote Metamagic

The there are the other metamagic feats, those that affect one mote each. If you only have one mote (by having skipped step 2), then these stack as noted in their descriptions. Otherwise you must pay for each mote feat once for each mote you want affected, either buying once per mote, or leaving some motes unaffected.

Examples

Enhanced, Twinned, Doubly Intensified lightning bolt (20th level caster): the base mote of lightning bolt is a line doing 10d6 electricity damage, as a 3rd level spell. Enhance (+4) is Slot metamagic, and one use affects the entire spell, increasing the basic damage from 10d6 to 20d6. Twin Spell (+4) makes this two motes, each being a line of 10d6 electricity damage. Because there are now two motes, Intensify may be bought once for each mote (otherwise it will only affect one), and so the caster has chosen to doubly Intensify, turning each mote into line of 240 electricity damage (now 240x2 damage, with electricity resistance counting twice), for +14 spell levels. The spell now needs a 25th level spell slot, but each of the first three slots of Improved Metamagic reduces this by 4 levels, then the next three reduce it by 2 levels. So three slots makes it level 13, and six slots make it level 7.

Doubly Enhanced, Quad (three Twins) fireball (30th level caster): the base mote of fireball is a burst of 10d6 fire damage, as a 3rd level spell. Enhance (+4) is slot metamagic, and so both purchases affect the entire spell (but bear in mind that you must have two feat slots of Enhance Spell to do this), turning the base mote into 30d6 damage for +8 levels. Quad Spell is three layers of Twin Spell, making three additional motes at 30d6 fire damage for +4 each, coming to +12 levels. The whole spell is then four fireballs of 30d6 fire damage each, all hitting the same spot at the same time, for a total of 23rd level. Up to three slots of Improved Metamagic would reduce this by five levels each, to a minimum of 8th level (4x30d6 damage, ranges 120-720, average 420, minus four times the opponent's fire resistance).

The better option, then is the Doubly Enhanced, Doubly Intensified, Twinned lightning bolt. The base mote is once again a line of 10d6 electricity damage, for 3rd level. Doubly Enhancing costs +8 levels and increases the base mote to 30d6 electricity damage. Twinning then makes an additional mote of that effect for +4 levels, making a total of two motes of 30d6 damage. Then both are Intensified, for +14 levels, making each a line of 360 damage. The spell then does 2x360 electricity damage (resistance applies twice), in a 29th level spell slot. The first three slots of Improved Metamagic reduce this by five levels each, the next three reduce it by two levels each. So with three slots of Improved Metamagic the spell requires a 14th level slot, and with six slots it requires an 8th level slot. Clearly if you have know Intensify and have enough slots of Improved Metamagic, this version is better.

Using the options I have introduced above, you can manage the following. Doubly Enhanced, Triply Intensified Violated flame strike (35th level caster): the basic mote of flame strike is a column of 15d6 damage, half fire, half divine, for a 5th level spell. Double Enhancement costs +8 levels and changes the base mote to 35d6 (proportions as above), requiring two slots of Enhance Spell. Triple Intensity costs +21 levels, increasing mote damage by 300% and maximising up to 600% (since we only have 400%, that's all of it), to a total of 420 fire and 420 divine. Finally Violate Spell turns half the damage into vile damage, costing +1 level and making the finished spell 210 fire, 210 vile fire, 210 divine and 210 vile divine (fire resistance only counts once). It takes up a 35th level spell slot (requiring Wis 45!), but the first three slots of Improved Metamagic reduce this by +3 each and up to 17 more reduce it by a further +1 each. A caster with three slots of Improved Metamagic can put the spell in a 26th level spell slot, and one with six slots can treat it as 23rd.

Bear in mind, however, that each of the above spells still count as their regular level (3rd or 5th), and so may be easier to save against or resist with SR than spells you might expect from such high level slots.