My recipe for better player retention:

• Offer and promote a draft mode with ghost cards and a cheap entry fee,
• Tournament is played in KO-System with 8 players,
• Create a set of specific reward cards which are SB and only usable as additional cards for this draftmode,
• Each participicant gets some of these rewards cards as prize, random bcx and random rarity like in reward chests,
• Winner gets main prize and runner up consolation prize funded by entry fee