in the cavity fig4 a illustrates an alternative embodiment of the trampoline bed accessory for either wet or dry play of the game mat 401 while it is filled with water as peripheral wall 414 retains sufficient water to initiate the deformation of rebounding mat 110 thus for wet play water peripheral wall 414 is initially filled with water via portal 441 deforming the rebounding mat after which water is directed to the central cavity between the peripheral wall to provide an open pool of water for jumping and splashing alternatively the trampoline bed accessory 401 may include other features associated with substantially dry play such as a game mat wherein the water retention in either or both wall 414 or central cavity is primarily to dampen the response of the rebounding mat 110 further enabling players to participate in the game mat activities more safely in a preferred embodiment the central region defined by peripheral wall 414 demarks a region of the game map 401 in a more preferred embodiment the accessory or game mat 401 includes an outer peripheral zone 445 having visual indicia 446 to indicate spacing for playing games and would thus extend to or even beyond the edge of the rebounding mat fig4 b illustrates another alternative embodiment in which the trampoline bed accessory or game mat 402 comprises plural layers of flexible and or elastic sheets that are sealed at the edge to form a substantially closed cavity 415 sides or edges of game mat 402 are optionally formed by sealing together at least an upper surface 405 and a lower surface 410 the lower surface intended to contact either the rebounding.