Eventually you should find the evil acorn. Get ready for a tough boss battle. After you talk to him, go through the door. Shoot Sigfried and the two bats that he spits. Hit him again. He'll be trying to suck you into the spikes that surround you and him. Quickly shoot him and he'll shoot a blob. Defeat the blob by shooting him. Follow this pattern. The second time he shoots a blob, he'll shoot a bat with it. On the third time, he'll shoot one blob and two bats. Beat them and hit him one more time to win. You'll get a present and a portal will appear. Grab the present and step into the portal.

Then go down through the next two doors. You'll be out of the Aztec Temple.