pvpstats_level - returns level
pvpstats_kills - returns kills
pvpstats_deaths - returns deaths
pvpstats_kdr - returns kdr
pvpstats_killstreak - returns current killstreak
pvpstats_topkillstreak - returns top killstreak
pvpstats_level_progress - displays progress bar
pvpstats_level_progress_percent - displays progress percentage
pvpstats_nextlevel_xp - displays amount of xp needed to progress to next level
pvpstats_currxp - displays current amount of xp
%pvpstats_kills_1% to %pvpstats_kills_10% - placeholders for custom statistics
%pvpstats_deaths_1% to %pvpstats_deaths_10% - placeholders for custom statistics
%pvpstats_killstreak_1% to %pvpstats_killstreak_10% - placeholders for custom statistics
%pvpstats_kdr_1% to %pvpstats_kdr_10% - placeholders for custom statistics
%pvpstats_hmr_1% to %pvpstats_hmr_10% - placeholders for custom statistics
%pvpstats_chr_1% to %pvpstats_chr_10% - placeholders for custom statistics
append with _amount to get amount, so: %pvpstats_kills_1_amount%

Using PlaceholderAPI? Your placeholders should look like %pvpstats_%

Using MVdWPlaceholderAPI? Your placeholders should look like {pvpstats_}