Revolt — When Renegade Rallier enters the battlefield, if a permanent you controlled left the battlefield this turn, return target permanent card with converted mana cost 2 or less from your graveyard to the battlefield.
2/9/2017 A permanent card is an artifact, creature, enchantment, land, or planeswalker card.
2/9/2017 The converted mana cost of a card in your graveyard is determined solely by the mana symbols printed in its upper right corner. The converted mana cost is the total amount of mana in that cost, regardless of color. For example, a card with mana cost has converted mana cost 3.
2/9/2017 If a card in your graveyard has no mana symbols in its upper right corner (because it’s a land card, for example), its converted mana cost is 0.
2/9/2017 If the mana cost of a card in your graveyard includes , X is considered to be 0.
2/9/2017 You can target any permanent card in your graveyard with converted mana cost 2 or less, not just one that was put there from the battlefield this turn.
2/9/2017 Revolt abilities check only whether a permanent you controlled left the battlefield this turn or not. They don’t apply multiple times if more than one permanent you controlled left the battlefield. They don’t check whether the permanent that left the battlefield is still in the zone it moved to.
2/9/2017 Revolt abilities don’t care why the permanent left the battlefield, who caused it to move, or where it moved to. They’re equally satisfied by an artifact you sacrificed to pay a cost, a creature you controlled that was destroyed by Murder, or an enchantment you returned to your hand with Leave in the Dust.
2/9/2017 Tokens that leave the battlefield will satisfy a revolt ability.
2/9/2017 Energy counters aren’t permanents. Paying won’t satisfy a revolt ability.
2/9/2017 All cards in the Aether Revolt set with triggered revolt abilities use an intervening “if” clause. A permanent you controlled must have left the battlefield earlier in the turn in order for these abilities to trigger; otherwise they do nothing. In other words, there’s no way to have the ability trigger if no permanent you controlled has left the battlefield that turn, even if you intend to have one do so in response to the triggered ability.
It's obvious, but someone has to say it, might as well be me
Keep your eyes on this card fellas.
Still these revolt cards depend so much on the enablers, without fetches or some other great enabler cards this may be a get tricky to get going.
In modern it does seem easy to get going and could be good enough.
In frontier this looks really strong.
I mean, this is better than Eternal Witness in many cases (relevant to Modern) and while I think its good that Wizards seems to know that mid-range decks are having issues in Modern, I can't help but look at this and think of all those blue mages who just realized how bad blue based interaction is now. I mean, if Mana leak wasn't cutting it for you before, think about how you'd feel if you Mana leaked a goyf turn two, just to turn around and see it pop back on the field from this?
As for your last statement, I wouldn't use mana leak on goyf early game. It would eat a removal spell, and then I would leak the creature with the ETB effect (unless the removal spell was path, then I probably don't care about a 3 mana 3/2), or the PW, or w/e. You should only play control if you are comfortable lining up answers to mitigate your opponents good lines of play.
Although TBH I don't play mana leak much because it doesn't really fit what I need. But I think cards like this are an argument in favor of mana leak rather than against it, since removal spells are generally worse than counterspells when your opponents creatures have ETB effects that matter.