The nature of reality bends a little differently in Arcadia than in Amber. The entire Discworld shows some of the behavioral traits of Primal Planes. Except in certain ways, the entire Discworld is highly resistant to the use of Primal Powers to mold and reshape it. The exception to this is the use of Primal Powers to reinforce the laws of dramatic necessity. Using Pattern to make a Million to One Shot (so long as the odds are in fact, exactly a million to one) is child's play, manipulating the Discworld so that one finds a dropped coin to buy a bagel is difficult beyond belief.
The Defensive and Sensory aspects of the Primal Powers seem to work just fine everywhere, though using Pattern or Logrus Sight near a Pattern is not a wise idea if you don't enjoy blindness.
One must move at least 3 days travel away from any of the Patterns in order to move into Shadow. This means that on the vast majority of the Discworld, one can move into or out of from shadow with ease. The Bride of the Jewel has been known to lockdown the shadow without warning, which means one must use Advanced Shadow Travel or else move to the very edge of the Discworld to travel, but she rarely does this.
Shapeshifting is a slightly risky business, as the odds of losing oneself in shifted forms is much, much higher than in the Amberverse.
Trump seems to work just fine everywhere, and a fair number of Discworlders have learned to make trumps which only work on the Discworld itself. (Pay-Per-Trump is growing in popularity.) The one exception is that trumping into a Pattern Chamber is a good way to get the Bride of the Jewel to show up and try to terminate you with extreme prejudice.
Magic, like the Primal Powers, seems influenced by the laws of dramatic necessity. Overuse of it weakens the fabric of reality and risks a breakthrough by the Things from the Dungeon Dimension (who are probably the Outsiders). Different regions of the Discworld have varying levels of magic. Most regions are normal mana zones.