The ornamental design for an underwaterlight-up diver toy, as shown and described.
FIG. 1 is a perspective view of an underwater light-up diver toy design;
FIG. 2 is a front elevational view thereof;
FIG. 3 is a rear elevational view thereof;
FIG. 4 is a right side view thereof;
FIG. 5 is a left side view thereof;
FIG. 6 is a top plan view thereof; and,
FIG. 7 is a bottom plan view thereof.
The broken lines showing portions of the underwater light-up diver toy design in FIGS. 1-7 are for illustrative purposes only and form no part of the claimed design.