Mime and Marionette seem to have changed a fundamental aspect of the Watchmen universe in Doomsday Clock #3. The two villains were introduced in Doomsday Clock #1 as being part of the same world that is the setting of Watchmen and were recruited by Adrian Veidt (aka the hero Ozymandias) to help him with a plan to save their world from nuclear destruction by locating the missing Dr. Manhattan.
Mime and Marionette were apparently introduced as analogs to the classic Charlton Comics villains Punch and Jewelee. Punch and Jewelee were originally puppeteers on Coney Island, as well as petty thieves, who stumbled across a box full of alien technology they decided to use in their crimes. The two comical villains frequently crossed paths with Captain Atom and Nightshade, who were re-imagined in Watchmen as the heroes Dr. Manhattan and Silk Spectre.
It was presumed that Mime and Marionette were, like Punch and Jewelee, ordinary humans with fantastic athletic skills but no actual superpowers. This seemed a safe assumption given that Dr. Manhattan was stated to be the only super being in the Watchmen universe. That seems to have changed, however, as Doomsday Clock #3 features a fight scene in which the invisible weapons Mime seemed to be pretending to be holding in earlier issues prove to be quite real and quite deadly.
This scene confirms what had merely been hinted before - that Mime has some sort of power to create whatever objects he imagines through sheer force of will. This was first suggested in Doomsday Clock #2, where Marionette asks if Mime brought his lockpick with him after the two are securely left locked up by Ozymandias and Rorschach. The two are shown to have escaped in Doomsday Clock #3, suggesting Mime's powers even before the fight scene that confirms them.
It is entirely possible, however, that Mime just has access to a set of invisible weapons and tools. The two criminals are insistent that they be allowed to retrieve their gear before escaping from prison in Doomsday Clock #1. This leads to a hilarious scene in which Mime is seen putting on his invisible weapons belt and brandishing an invisible gun before a dumbfounded Rorschach. This begs the question - what if he really DOES have a bunch of wonderful invisible toys? This concept certainly would be more in-line with the original concept behind Punch and Jewelee and make them more of a match for The Joker, whom the duo are now seeking out.
There is a third possibility to be considered - that the journey between Earths may have awakened Mime's metagene and given the madman a power that he and his equally crazy wife always thought he had before. Mad as that idea may sound, there is a precedent in previous DC Comics stories. Dinah Drake, the first Black Canary, mysteriously developed her sonic scream power after traveling from Earth Two to live on Earth One during The Bronze Age of Comics. Further, metagenes have been shown to act upon subconscious triggers in the past, causing a person to develop powers based on whatever was on their mind at the time.
Source: Doomsday Clock #3