  We find transient, transit-like dimming events within the K2 time series
photometry of the young star RIK-210 in the Upper Scorpius OB association.
These dimming events are variable in depth, duration, and morphology. High
spatial resolution imaging revealed the star is single, and radial velocity
monitoring indicated that the dimming events can not be due to an eclipsing
stellar or brown dwarf companion. Archival and follow-up photometry suggest the
dimming events are transient in nature. The variable morphology of the dimming
events suggests they are not due to a single, spherical body. The ingress of
each dimming event is always shallower than egress, as one would expect for an
orbiting body with a leading tail. The dimming events are periodic and
synchronous with the stellar rotation. However, we argue it is unlikely the
dimming events could be attributed to anything on the stellar surface based on
the observed depths and durations. Variable obscuration by a protoplanetary
disk is unlikely on the basis that the star is not actively accreting and lacks
the infrared excess associated with an inner disk. Rather, we explore the
possibilities that the dimming events are due to magnetospheric clouds, a
transiting protoplanet surrounded by circumplanetary dust and debris, eccentric
orbiting bodies undergoing periodic tidal disruption, or an extended field of
dust or debris near the corotation radius.
