I usually see them on Jakarta city birthday celebration, and for me they're quite eerie , children usually get scared of them, and this is a little bit history about Ondel2
"In the past, they were used to protect the community from black magic and afflictions. The two puppets symbolize the spiritual protection provided by the ancestors to the Betawi population"
A pair of ondel-ondel, consisting of a male and female puppet, takes about a week to make. The process requires patience and good observation. The first step is preparing the puppet's skeleton, which is made from 400-centimeter-by-1.5-centimeter bamboo twigs. The mask of a male ondel-ondel is usually painted in black or red. The puppet is dressed in a black top and sarong. The mask of a female ondel-ondel is usually white.
(source taken from: the jakarta post)