You can reveal 1 other "B.E.S." monster in your hand; Special Summon this card from your hand, then place 3 counters on this card. During the Main Phase (Quick Effect): You can remove 1 counter from this card and activate 1 of these effects;
• Add 1 "Boss Rush" or 1 Spell/Trap that mentions it, from your Deck to your hand.
• Special Summon 1 Level 9 or lower "B.E.S." monster from your GY.
You can only use each effect of "B.E.S. Derringer Core" once per turn.