Q: Elephantopus says „The opponent cannot block with creatures with power 4 or less.“ What happens when I have a creature with Hunter, and I choose to attack a creature with power 4 or less.
A: With a Hunter, you can still hunt down any creature you want. The Elphantopus only prevents the opponent from choosing a creature as a blocker.
However, using the Hunter ability is optional. So if you chose to not use the Hunter ability on your attack and the opponent only has creatures with 4 or less, your Hunter would be unblockable.