Sometimes objects don’t lend themselves to using tradition wall fasteners to attach object to the wall, such is the case with paper mache letters.
Try aligning a long string of letters with wall anchors and it will soon appear you were inebriated when attempting the task. You could use VHB or high bond foam tapes, but they don’t let you reposition the work, and when it comes time to remove, they could remove part of your wall. Command Strips could be an alternative, but they require two stage install, and will be difficult if repositioning is needed. They are also pricey. An alternative solution is using Apartment Tape. On one side it has high bond adhesive to attach to the object and a removable adhesive side that is used for the wall side. If you don’t have the object just right, you could remove and reposition. You could cut if needed, and when ready to remove from wall, there will be no foam residue left behind.