It's because there are limits, that it can bloom beautifully.
[AUTO]:When this unit is placed on (RC) or put on (GC), [COST][retire one or more of your other back row rear-guards], and this unit gets [Power] +5000/[Shield] +5000 until end of turn for each unit retired for this cost. If you retired two or more units for this cost, [COST][put two normal units with "Musketeer" in their card names from your drop on the bottom of your deck in any order], and draw a card.