On a Roll
Interact with the playground somehow.
Use the gravity gloves to intercept an incoming enemy grenade in mid-flight.
Kill a Combine Heavy while their shield is up.
Use the gravity gloves to loot an item off a living Combine soldier.
Pick up and smash 50 glass bottles.
Snatch a Xen grenade from its resting place.
Use the multitool to hack a tripmine.
Collect the SMG.
Kill a grunt by shooting their gas tank.
Feed the snark.
Zombie with a Shotgun
Collect the shotgun.
Receive a tasty treat.