  We report on the Neutron Star Interior Composition Explorer (NICER)
monitoring campaign of the 468 Hz accreting millisecond X-ray pulsar IGR
J17379-3747. From a detailed spectral and timing analysis of the coherent
pulsations we find that they show a strong energy dependence, with soft thermal
emission lagging about 640 microseconds behind the hard, Comptonized emission.
Additionally, we observe uncommonly large pulse fractions, with measured
amplitudes in excess of 20% sinusoidal fractional amplitude across the NICER
passband and fluctuations of up to ~70%. Based on a phase-resolved spectral
analysis, we suggest that these extreme properties might be explained if the
source has an unusually favorable viewing geometry with a large magnetic
misalignment angle. Due to these large pulse fractions, we were able to detect
pulsations down to quiescent luminosities (~5 x 10^33 erg s^-1). We discuss
these low-luminosity pulsations in the context of transitional millisecond
pulsars.
