Can Powers target lands where it's impossible to resolve all of the effects (e.g., Spreading and Dreadful Mire targeting a land without Dahan)?
Can Powers target lands where it's impossible to resolve all of the effects (e.g., Spreading and Dreadful Mire targeting a land without Dahan)?
Yes, Powers just need to be able to meet the conditions in the "Range" and "Target" boxes.
In this Spreading and Dreadful Mire example, the only targeting restriction is having Invaders. While some thresholds of the Power will push Dahan if possible, Fathomless Mud of the Swamp isn't required to target a land with pushable Dahan.