So far, we have the Goliath, who breathes fire, and the Kraken who generates lightning.
Alternatively, we have Hyde, who has a flamethrower, and Markov, who has a lightning gun.
In a video interview with IGN, the developers stated that certain hunters will be more useful against certain monsters than others.
Could it be that the Goliath would be immune to the flamethrower, and that the Kraken could be immune to the lightning gun? How effective would shooting lightening at something that generates and manipulates lightning really be?
If this is indeed the case, thinking of what the third monster might be immune to could give us a good hint towards what it might be.