The Winter Wonderland map of the popular game Half-Life: Opposing Force has the feature of remodeling snarks as deadly penguins. For the unfamiliar, snarks are nasty little one-eyed alien cockroaches which can be carried as weapons. Upon deployment, a snark will enthusiastically seek, chase, and bite nearby players (including you, if you're not careful). After a brief delay, it will explode in a greenish spat of toxic death, similar in strength and appearance to the spore gun projectile. The penguins function identically, except that they explode with the effect and damage of conventional grenades. Close examination of the weapon model (possibly high-definition pack only?) reveals that the penguins in fact have small grenades strapped to their backs.
There is only one pickup for the pengin in Winter Wonderland, next to the only pickup for the displacer. This is on a ledge in more or less plain view, which is reachable only by clever use of the barnacle grapple. The penguin pickup itself appears as a human-sized snowman wearing a top hat and holding a sign which reads "Beware the penguins!".