Krishna took initiative to know the death secrets of BHISHMA to eliminate a stronger general.
Even Lord Krishna encouraged, as per present terminology we call Horse Trading. KARNA'S camp too he visited with an intention. He tried to motivate KARNA to join with pandavas, as he being the eldest son of Kunti.
KARNA was a man of words. He refused to switch sides. Karna told Krishna, his loyalty is with DURYODHANA. On receiving refusal from Karna, Krishna took the help from INDRA which in turn took away the body armor from Karna. So that he could be killed easily by ARJUNA. Generous sacrifice of karna invited death for self.
SUDARSAN CHAKRA was used by KRISHNA to create an artificial sunset so that Jayadrath could be killed.
There are many such occasion and situations where Krishna's tactical support, helped PANDAVAS to win over the situations and finally the war of MAHABHARAT.