When you tap it, you add X mana of any one color, where X is the greatest number of creatures you control that have a creature type in common
This is because it costs zero mana and immediately replaces itself in your hand once your opponent starts
Even though your opponents get to take a peek at what youre drawing, they all lose life equal to the cards mana value as well, helping to whittle away your opponents life totals.
There are a lot of sideboard options available to you, but to run through a few I particularly like, I do think Dive Down gets a lot better in sideboarded games if you know your opponent will be dense on removal for Games 2 and 3, so whilst maindecking this card is unappealing I have enjoyed having access to the card in my 75
Ramp & Card Draw Ramp and card draw are two intrinsic columns of deck building, and perhaps two of the most important facets that Commander decks share
Waterbenders Restoration is an option I like quite a bit