Considering this card as an occasional that makes white an interesting splash color for madness and selfmill decks:
But I fear that it is GRBS. Any opinions?
It's a strong effect, but you need to have 3 mana open, which is a lot.
In practice, it's a Mother of Runs variant and the more you have to pay for the effect, the weaker they are. Affecting the whole team is less important than the cost is but the chance of making your whole the unblockable does give it an interesting edge. Note that you will get a creature blown up in response when you do.
The main issue is getting it into the bin. White can't do that and colours that do aren't likely to be interested in a white card. Madness decks also tend to discard lands so the effect is a bit too expensive for them. In practice, I think it's going to be a multicolour card, I would say WG or WB.
It never saw the most play, but, back in the day, I think it was played in GW madness decks and some midrange, value decks, perhaps with Survival of the Fittest, even.
Still if you want a similar effect, you have this:
It's better than it seems like, particularly the back. A free instant from the graveyard hurts!