An entity that disappears a few ticks after being summoned. Additionally, the log when it is summoned reads "Summoned new Falling Sand."
/summon alexscaves:falling_frostmint
/summon alexscaves:falling_guano
It can be summoned but continues to exist as an invisible entity.
I'm not sure if this is intended behavior, but I think it would be better if it disappeared when summoned without the necessary values specified.
/summon alexscaves:falling_tree_block