It is the viscous drag of the co-moving solid-like fluid blob around the intruder that decelerates said intruder impacting a cornstarch suspension, not the added mass or surface tension. A nice puzzle to solve! Thanks Scott for sharing original data.
Marc-Andre Brassard, Neil Causley, Nasser Krizou, Joshua A. Dijksman, Abram. H. Clark — Journal of Fluid Mechanics 923 (2021)
MultiPhase Matters 