  We propose a novel method to constrain turbulence and bulk motions in massive
galaxies, groups and clusters, exploring both simulations and observations. As
emerged in the recent picture of the top-down multiphase condensation, the hot
gaseous halos are tightly linked to all other phases in terms of cospatiality
and thermodynamics. While hot halos (10^7 K) are perturbed by subsonic
turbulence, warm (10^4 K) ionized and neutral filaments condense out of the
turbulent eddies. The peaks condense into cold molecular clouds (< 100 K)
raining in the core via chaotic cold accretion (CCA). We show all phases are
tightly linked via the ensemble (wide-aperture) velocity dispersion along the
line of sight. The correlation arises in complementary long-term AGN feedback
simulations and high-resolution CCA runs, and is corroborated by the combined
Hitomi and new IFU measurements in Perseus cluster. The ensemble multiphase gas
distributions are characterized by substantial spectral line broadening
(100-200 km/s) with mild line shift. On the other hand, pencil-beam detections
sample the small-scale clouds displaying smaller broadening and significant
line shift up to several 100 km/s, with increased scatter due to the turbulence
intermittency. We present new ensemble sigma_v of the warm Halpha+[NII] gas in
72 observed cluster/group cores: the constraints are consistent with the
simulations and can be used as robust proxies for the turbulent velocities, in
particular for the challenging hot plasma (otherwise requiring extremely long
X-ray exposures). We show the physically motivated criterion C = t_cool/t_eddy
~ 1 best traces the condensation extent region and presence of multiphase gas
in observed clusters/groups. The ensemble method can be applied to many
available datasets and can substantially advance our understanding of
multiphase halos in light of the next-generation multiwavelength missions.
