If you buy a priest rank 1 idol, summon the priests, sell the idol, buy rank 2 idol, summon priests you will end up with 4 priests. You can repeat this up to rank 4 and end up with 8 priests, all of which will heal you on different timers (making you near invulnerable).
However, the low rank priests die pretty easily and you can't resummon them (without re-purchasing the idol) so it's not actually terrible unbalancing, even wtih Sedna. It is also fun running around with 28+ minions. 