2600 Version
In the first ruins level, after bouncing off the first tongue, jump as far left off the platform as you can. kill the scorpion and go through the door, and after getting the letter, jump left and play the original Pitfall.
Unlimited Explode stones
Near the end of the last ruins level, there is a segment of platform with a totem and two hanging pots. One has a life and the other an exploding stone. Get both and jump off the platform to reappear on the totem. Do this until you have 99 stones, then go and easily defeat warrior spirit.