Edit: You can find new and improved optional rules for Channelling in version 2 here.
Channelling in WFRP 4e needs a little love. It seems fine on paper, but in reality it’s much better to concentrate on using and improving your Language (Magick) skill and getting better at casting, than it is to even bother with channelling in most cases.
So with that in mind, here are some optional rules to give channelling a little push in the right direction. I would love to hear if any of you use them in your own games, or if you have different house rules in place?
Controlling The Swirling Winds
If your GM has rolled for The Swirling Winds (page 238 of WFRP 4e), you may spend your Action channelling to alter the magical energy available. For every 2 SLs on a successful Channelling test, you may change the strength of the Wind appropriate to your Channelling skill by one step. The difficulty of the Channelling test is modified by The Swirling Winds as normal and characters using the ungrouped version of Channelling affect and are affected by all of the Winds at once.
Example: Berchtold has used his Second Sight and noticed that the Winds are blowing weakly and so any casting or channelling test currently has a -30 modifier. As he is a wizard of the Grey Order, he attempts to channel Ulgu into the area to make channelling and casting with Ulgu easier. His Channelling (Ulgu) is 87, but with that -30 penalty he only has a slightly better than 50% chance to even succeed. Luckily for Berchtold he rolls a 32, which gives him 2 SLs. That’s enough for him to channel a sufficient amount of Ulgu into the area to drop the casting and channelling modifier from -30 down to -10. It’s still not going to be as easy as he would like, but it’s definitely better than before. Next turn he can choose to try again, but this time will only be at a -10 penalty to the Channelling test. Another Grey Wizard, or a Witch would also benefit from the reduced modifier.
Once a character has learned an Arcane Magic talent they may deliberately attempt to overcast a spell by channelling extra magical energy into it first. This is useful if you need the certainty that your spell will have extended range for instance.
To Over Channel the caster selects the number of overcasting SLs they need and only stops channelling once those additional SLs have been reached, after reducing the CN.
If a wizard Over Channels a Petty Magic spell in this way it gains the benefits of the Lore specific effects associated with Arcane spells from their Lore. It is a stepping stone for wizards that have newly gained the Arcane Magic talent and have not yet learned any of the more powerful spells available to their Lore, but are capable of applying the basic principles to spells they are already familiar with.
Sometimes expediency is more important than spending a full action to channel. A caster may optionally use their Move Action to channel instead of using a Standard Action, but are automatically considered to have been interrupted and must pass a Hard (-20) Cool test or suffer a Minor Miscast.
When channelling in this way the caster is not required to reduce the CN to zero, but must cast the spell as their Standard Action immediately afterwards at whatever the CN happens to be after the channelling attempt.
Example: Berchtold is in a bit of a bind (surrounded by thugs) and wants to cast Shadowstep to get away from the action. Shadowstep is normally CN 8, so any successes he can score on a Channelling test will help. He passes his Cool test and rolls a 54 on his Channelling test, scoring 3 SLs and reducing the CN to 5. For his action he must now cast Shadowstep, but only needs 5 SLs on the casting test to succeed and disappear into the shadows.