"Overload your opponent too" is probably the only mechanic that would make most of the existing Overload cards viable. It would also be frustrating as hell with cards like Elemental Destruction. A nice idea (it keeps popping up in the card creation contest) but I give it very little chance of becoming an official card. The reason is that Blizz tends to be reluctant with effects that limit your opponent's options, like discarding cards from his hand. Right now, the only way to destroy an opponent's mana crystal is to play Darnassus Aspirant into his Mirror Entity.
And by the way, a 2 mana 0/8 totem with "can't be targeted by spells or hero powers"? ... Shaman dream but not going to happen either. If this makes it into the game, it would be closer to Flametongue Totem.
This is so obviously broken I'm surprised you're even asking if it's OK.
The effect is better than card draw and and you and your friend give the "Mana Tide Totem" 1 less mana, +5 Health and "Can't be targeted..." . Why it's Legendary makes even less sense, legendaries have strong connection with lore and individuals. And giving your opponent Overload is in the same street as discarding your opponent's cards, something Blizzard has clearly stated they don't want, because it's nothing you can do against it and just becomes boring playing against