  We extend the motion-planning-through-gadgets framework to several new
scenarios involving various numbers of robots/agents, and analyze the
complexity of the resulting motion-planning problems. While past work considers
just one robot or one robot per player, most of our models allow for one or
more locations to spawn new robots in each time step, leading to arbitrarily
many robots. In the 0-player context, where all motion is deterministically
forced, we prove that deciding whether any robot ever reaches a specified
location is undecidable, by representing a counter machine. In the 1-player
context, where the player can choose how to move the robots, we prove
equivalence to Petri nets, EXPSPACE-completeness for reaching a specified
location, PSPACE-completeness for reconfiguration, and ACKERMANN-completeness
for reconfiguration when robots can be destroyed in addition to spawned.
Finally, we consider a variation on the standard 2-player context where,
instead of one robot per player, we have one robot shared by the players, along
with a ko rule to prevent immediately undoing the previous move. We prove this
impartial 2-player game EXPTIME-complete.
