You wouldn't believe how many plots to kill Castro were considered. The CIA actually had a big list of possible ways to do it (some were attempted, some were not) the craziest of which included the following.
Slipping him an exploding cigar. Not one of the little joke ones, either. The one they devised for the job would blow a good chunk of your face off and send teeth into the back of your throat like shrapnel.
Planting a special pen into his office that, when the thrust tube was depressed, would send an ultra-fine poisoned needle that he wouldn't even feel into his thumb.
Attempting to exploit his love of scuba diving two plots were devised. One was to plant explosives in an exotic shell hoping Castro would attempt to collect it. The other was to contaminate his diving suit with a fungus that would cause painful and debilitating skin conditions.
Attempting to drug him with hallucinogenics or amphetamines to destabilize Castro's mental state. It was believed that this would prompt one of his own generals to assassinate him fearing that Castro was no longer capable of leading the country.
They even considered attempting to undermine his image as a strong leader in the eyes of the Cuban people by, again, drugging him before a speech.... or lacing his shoes with Thallium to make his beard fall out.