Many spells change the size of a person or creature, or creatures have their size altered to suit the story needs of an Ars Magica saga. I’ve been asked several times about changing size in the last month (mostly because my blog post on gigantism had an error) so here is what I’ve sussed about it. Broadly speaking the spell mechanics are variable, so please see your story-guide.
- Each +1 mag in spell design will add 3 size levels (note some spells sampled from the core books seem to use +2 levels instead, but there has been much discussion and the fair middle ground seems to be +3 per mag).
- Each +1 mag in spell design will reduce size by 6 levels (again variable by books, some spells seem to be able to reduce by a far greater amount than increase, I think that is primarily because once a creature is smaller than size -4 they have such low wound levels than it is almost moot).
- Each +1 Size = +2 Strength, -1 Quickness, +1 point in the wound level damage ranges (see HoH:MC p. 39).
That means changing a soldier from normal (size +0) size to size +2 adds 4 strength, subtracts 2 quickness, and alters their first “light wound” damage range to 1-7 points instead of 1-5. That might not sound like much of a change but it makes the soldier far more offensively oriented. Slower, harder to kill, and able to inflict more damage.
This is also why reducing an opponent down to -3 or smaller is very effective, it might make them quicker but they have radically reduced wound levels for penalties, which is savage in a prolonged battle.
There is also a point at which the difference between the attacker and defender becomes so extreme that the defender really shouldn’t be able to “parry” to defend.
A rationale is: A mouse can avoid the boot of a man easily due to speed, but if the man successfully steps on it, then it really should be dead, or mostly dead.
So how big does your shield grog need to be to just squish opponents? Well I’m not sure. The size increases are meant to be 10x larger per 3 size ranks, but there is not a formula that shows how tall a person is per rank (a project for a rainy day?). Size 0 human vs a size 10 dragon seems altogether a massive challenge.