Cancellation of the gravitational force is a long favorite experiment of sci-fi writers, but as far as in our knowledge, nobody considered the case of gravity force acting in the horizontal direction.
“Gravitus Horizontus” is the magic spell used by Magica de Spell in A Matter Of Some Gravity. She learned it in a magicians’ meeting in Lucca (probably referring to Lucca Comics): the spell cause a temporary modification in gravity’s arrow against people affected by the spell. In this case Donald and Scrooge experiment a horizontal gravity, toward the walls of the money bin.
Don Rosa doesn’t specify, from time to time, if there is a new center of gravity, so that walls, palaces, mountains attracted Donald and Scrooge with a horizontal force.
More likely it is the terrestial gravity which acts again, after a local rotation of the versus of the force, as suggested by Donald Duck’s quotation while the two ducks are in Scrooge’s office:
This furniture only looks like it’s nailed down! I’m too heavy for it!
Later Donald’s nephews exploit the effect to give chase to the witch:
We can steer our wagon at high speeds if you pull it with your weight!
The explanation is simple: the motion of the cart is horizontal, as the force acting on the ducks. So the nephews attack the uncles to the cart, and the two ducks “jump” across the building corner in the right direction. The cart is pushed in that direction by a horizontal force equals to the weight of the two ducks, with a resulting acceleration $a = g/2$, if nephews and cart total mass is equal to uncles total mass, or even larger if the two ducks are more heavy than the load they drag.
Another interesting point is crossing lake by our heroes. Scrooge jump in the water, suck that to stop their horizontal fall using the friction of the water, just as a spaceship speed is slowed down entering the atmosphere from an orbital flight.
At last Magica is reached at the airport, so the witch strikes again: “Gravitus opponere!” After that spell the gravity arrow points upward so the ducks are driven away from Earth, but the nephews climb up the uncles’ feet together with a fire estinguisher. In such way the total mass of nephews and estinguisher equals uncles’ mass, balancing the upward and downward forces. When nephews open the estingusher, the jet stream pushes them into the sky, so a “jet-propelled duck group” approach the aircraft stolen at airport by Magica and get the possibility of overcomind the witch in the final fight.
The most intriguing point for a physicist is that the spell is a parity violating interaction, i.e. the effect does not show specular symmetry: the ducks can go down the steps because they are pushed rightward the step vertical side, moving from upper right to lower left. This would not happen if they had to climb down moving from upper left to lower right. Luckly the airport is in the right direction.
It is worthwhile noting that Don Rosa was aware of this point, and later he exploited it in a gag: the ducks are supported by the windshield in one way, and flight away toward the back window when the bus u-turns at the airport bus stop.