If your just trying to unlock all champs buy the hextech mystery champion shard

after u've finished buying all champs that are 4800 ip or less. since 1 mystery shard is 1700 ip and u need 3 for a random champ that would cost 5100 ip instead of 6300 ip to buy the champ. use champ shards that give less blue essence if u need it for unlocking mastery levels.