The ornamental design for an inflatablecostume, as shown and described.
FIG. 1 is a front, right and top perspective view of an inflatable costume, showing my design.
FIG. 2 is a front elevation view thereof.
FIG. 3 is a rear elevation view thereof.
FIG. 4 is a left side elevation view thereof.
FIG. 5 is a right side elevation view thereof.
FIG. 6 is a top plan view thereof.
FIG. 7 is a bottom plan view thereof; and,
FIG. 8 is another front, right and top perspective view of the inflatable costume in a usable state.
The broken lines depict portions of the inflatable costume that form no part of the claimed design. The broken lines in FIG. 8 depict environment and form no part of the claimed design.