I think it's very important that this ability exist in the game. It takes spellcasters down a notch (often quite literally), but more importantly it can be the PCs' best line of defense against an enemy spellcaster. If you can't interrupt his Sleep spell, well, a low level party is screwed. Generally it's a good defense against casters being overpowering and gives parties a fighting chance, but I don't like AD&D's rather difficult way of achieving it.
Swords & Wizardry has a simple system. Spells being cast start at the beginning of the round, and go off on the caster's initiative. So if a spellcaster loses initiative and gets hit, this interrupts the spell. Easy peasy. There is a more complex method that involves taking a full round to prepare a spell, at which point the caster can be interrupted by damage, and once readied the spell can be cast when the magic-user is ready. Not quite as easy.
Adventurer Conqueror King expands this to damage or failed saving throws interrupting spellcasters. Lamentations of the Flame Princess puts more or less the same rule in different terms: if a character takes any damage in a round, they can't cast a spell after that. It's not a proper interrupt, but it serves basically the same purpose.
OSRIC has a cleaned-up interpretation of the AD&D rules, while BLUEHOLME, Labyrinth Lord and Basic Fantasy RPG just follow their Basic versions in neglecting this area.
The interesting choice here is how Swords & Wizardry and ACKS both assume that the spell is specifically interrupted and lost, while LotFP merely forbids spellcasting once damage is taken. The former approach is harsher on the magic-users, to be sure, and rooted in AD&D, where being hit can likewise cause spell loss. Neither proposes any kind of roll (such as a saving throw) to see if the spell can be kept; it is simply gone. I think this is a good compromise between the harsher S&W / ACKS approach and LotFP's method.
Another possibility I haven't seen explored much is that the attack causes a misfire of the spell. This is always a good excuse to pick your favorite "haywire spell effect" table and roll on it, to reflect the magical energies that have been let loose by the incomplete incantation. These should be used sparingly, and perhaps only have a certain percent chance (maybe 5%-10% per spell level) so that it doesn't devolve into complete unpredictability.
Whichever is your favorite, I think these are the most straightforward spell-interruption rules out there, and deserve consideration for any OD&D or classic D&D game.
There are so many ticky-tacks in RPGs. Must think upon this: should a wizard be allowed a save to keep his spell?
ReplyDeleteI allow wizards to cast spells they have not prepared; but they must save or die before the spell goes off. In a dire situation where you will probably die anyway, it's a nice option.
Simple B/X or LL house-rule: move spell casting to the last thing in the round for both sides, after each side has taken missile and melee steps. Spell casting is declared and begins at the beginning of the round (no moving on a round one is casting). If hit in the missile or melee steps, the caster must make a saving throw versus Spells or lose the spell. Any spells that go off then go of in the order of the opposing casters initiatives; if a caster is then his by a spell, if it is damage he must make a saving throw or lose his spell; otherwise, it depends on the nature of the spell he is hit with...
ReplyDeleteOld School Hack has fixed phase combat rounds: Spellcasting starts after missile combat, commences through the remainder of the round (where moving, melee, and pushing/throwing people happens). If the spellcaster is neither hurt nor tackled, the spell takes hold at the end of the round.
ReplyDeleteTo me the S&W rules make the most sense, and are the most straight forward to remember.
ReplyDeleteI put a lot of value on card-game-style group initiative (play goes from the dealer/referee's left around the table) to keep things manageable and moving, so most of the usual approaches don't work well for me.
ReplyDeleteUsually, the rule I use is that one of the possible actions is to "cover" an opponent, attacking or using a counterspell if they make a watched-for action during their next turn, which will cause them to fumble (or at least be very likely to fumble) whatever they were doing, whether that's moving, attacking, using a spell, or whatever.
On my blog, I wrote up a simple solution for expanded spell casting interruptions in D&D 5e:
ReplyDeletehttp://ragingowlbear.blogspot.com/2014/07/dnd-5e-spell-casting-interrupts.html