Basically save your science lab from being destroyed by your creation (or letting the creation escape, or whatever other incentive is chosen)
Each level is a room/area
Obstacles already exist (e.g. walls)
There are valuable things in the level that cannot be destroyed or you lose
Maybe windows that have to be avoided so thing doesn't escape
Goal is to get creature back in cage before it destroys important things in the level or escapes or whatever
The level starts w/ the creature moving a tiny bit in a certain direction, then everything pauses
Players have a toolbox of things they can use to slow the thing down and/or change its direction
Some things change speed/directions predictably (some randomly in single-step mode)
Amount of items in toolbox is part of the challenge
Two ways to play (not sure if valuable to provide both, or pick the best gameplay)
Single-step mode allows one placement at a time. Creature pauses after each hit (be it a in-room obstacle or something placed). During pause, player can place a single item and manually resume.
Full-prep mode allows player to setup all the placements and then, when run, the full thing goes bouncing off of everything until it's trapped or out of steam (prevent infinite recursion) or hits valuable things (or exits via window or any scenario)
Multiplayer approaches:
Alternating turns
Adversarial w/ another player actively trying to destroy the lab, let the creature escape, prevent capture, etc
Only applicable for single-step mode
Coop with each player having different toolboxes of things to choose from
Level designer would be essential since there needs to be enough levels to make it worthy
Ability to gen random levels would be nice too of course