The lion has seen the goat which is used as a bait and IS WALKING straight into the trap set up for it.
Is there a rule that says that "present perfect tense must go with a present continuous tense" as in the sentence above. Is it so? Would a simple present tense "walks" gives a better sentence than "is walking" does ?
There is no rule; the present continuous is used here to show the action is in progress. You could say 'walks', but that would imply that the animal started walking at the time of speaking, while the original suggests was on its way at the time of speaking.