One of the biggest disappointments in the Sega Genesis version of Ecco the Dolphin was its lack of informing how important it is to get the ancient songs of wisdom.
Not only do the special songs allow Ecco to defeat his enemies quickly and confuse sharks but he can also absorb their "Souls" preventing them from re-spawning in the level again, there are however exceptions to this power.
The ancient songs of wisdom work in both Ecco the Dolphin and Ecco 2: The Tides of Time. The only song that doesn't work in Ecco 2, is the song for confusing sharks.
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When Ecco saves the Dolphin's in the levels The Lagoon and The Vents he receives special songs that give him new abilities.
If you save all the Dolphin's in The Vents you get a special song for attacking your enemies, sometimes referred to as the charge sonar. To initiate it press the charge button and then quickly press the sonar button.

In the level The Lagoon saving all the Dolphin's gets you a special song used to confuse the hungry ones or sharks. To use it simply sing to a shark and it will hold still moving back and forth making it easy for Ecco to attack.

After gaining at least one of the ancient songs of wisdom from either The Lagoon or The Vents, Ecco gains an undocumented ability to absorb enemies souls. To absorb an enemies soul attack the enemy with a charge or charge sonar and hold down the charge button after the enemy dies.
The stars that appear when an enemy is defeated are absorbed by Ecco, instead of just vanishing. What this special ability does is prevents enemies from re-spawning after they are killed.

In Ecco the Dolphin for Sega Genesis there are two levels where you have to save Dolphins in order to gain ancient songs of wisdom needed for the rest of Ecco's journey.
A great short cut for both The Lagoon and The Vents is to find the easiest to save Dolphin first, then initiate the cheat menu and write down the x and y teleport locations. Return the Dolphin back to its family then initiate the cheat menu and enter the x and y teleport locations you wrote down.
You will find the same Dolphin has returned to be saved again, return him back to his family and repeat this cheat until enough Dolphins have been saved that the leading Dolphin thanks you.
Even though you saved the Dolphin, this cheat works because the computer forgets to remove the Dolphin from the location rescued. This can work with any rescued Dolphins in any of the levels since all their locations are reset.
Related: Interesting Things in Ecco the Dolphin - 07-27-2009