So having issues in version 1.13 with placeholders. just dumping them here (well the ones i use).
%statistic_player_kills%
%statistic_time_played%
Most of the Entities for killed/kill
%statistic_kill_entity_% (example bottom)
%statistic_kill_entity_GHAST%
i guess Statistic mine and use items... mostly stats.
%statistic_mine_block_COAL_ORE%
%statistic_use_item_COAL_ORE%