  This paper is focused on the transition phase between central stars and white
dwarfs, i.e. objects in the effective temperature range 100,000 - 200,000 K. We
confine our review to hydrogen-deficient stars because the common H-rich
objects are subject of the paper by Ziegler et al. in these proceedings. We
address the claimed iron-deficiency in PG1159 stars and [WC] central stars. The
discovery of new Ne VII and Ne VIII lines in PG1159 stars suggests that the
identification of O VII and O VIII lines that are used for spectral
classification of [WCE] stars is wrong. We then present evidence for two
distinct post-AGB evolutionary sequences for H-deficient stars based on
abundance analyses of the He-dominated O(He) stars and the hot DO white dwarf
KPD0005+5106. Finally, we report on evidence for an H-deficient post-super AGB
evolution sequence represented by the hottest known, carbon/oxygen-atmosphere
white dwarf H1504+65 and the recently discovered carbon-atmosphere "hot DQ"
white dwarfs.
