You can push bosses, mobs that survive the throw, players, skull champs, and vehicles with the Christmas spear throw.
I AM NOT TRYING TO MAKE PEOPLE DO THIS
In Victoria Harbor a skull champ spawned and 2 spears were thrown right on it. The push with the spears made it so the champ was pushed into the water killing it. BTW I also found out that splashy washy pushes the champ back a bit too.
In king cake boss the spear pushed the cake off the map
In pvp I got launched
Have fun with this info, abusing with Christmas spear