Red:
Yes, Rubbling Ruin. I don't think this card is being criminally under rated, but I think it's worth highlighting how good it is. In Gruul with a high density of riot cards, it basically reads 'your creatures are unblockable this turn' and you get a 6/6 added to the board if you somehow didn't just win the game. I'm looking to grab this over most other cards if I have the riot enchantment in my pool. I'm happy to splash for this in my Simic decks to pair with Adapt as well. It's floor is a 6/6 for 6, which is perfectly fine.
2 on the cusp:
Similar to
Clear the Stage, Flames of the Raze-Boar is an easy top 5 in a deck with a reasonable amount of 4+ power doods. I'm happy to pick this up in Gruul. In Rakdos, it's more often an overpriced burn spell and I'd probably prefer
Consign to the Pit at the same mana cost but killing anything. Dagger Caster is a card I always want in my sideboard, but not always maindeck. It's amazing in some matchups (hoses Afterlife tokens, every color has at least one 1 toughness creature, and it combos with
Bladebrand for a 1-sided board wipe), but if opp only has 2+ toughness creatures it feels bad as a 2/3 for 4.
Honorable mention:
Gates Ablaze and
Spear Spewer. These two range from super good to super garbage, depending on your build. In a gate heavy deck, Ablaze can be a cheaper and easier to cast
Kaya's Wrath. Pair with the gates Ram to have a loan fatty on board after the wipe. In other decks it can be a 3 mana do-literally-nothing spell. Spewer can be really good in a spectacle heavy deck. You can cast
Hackrobat T2 (albeit rare occurrence) with it, and being able to turn on spectacle for free even when you have bad attacks is extremely valuable. I might even run this if my deck only has a few spectacle cards and I'm short on playables, but I'm never running this in Gruul or splashing for it.
Green:
Yes, Sauroform Hybrid. Like Rumbling Ruin, I don't think it's being criminally under valued, but I do think it's top 5 good. You want some 2 drops in your deck and it doesn't get much better than this at common/uncommon. It scales late, making it an amazing top deck for a bear. Incidentally, this Adapted T6 followed up by Rumbling Ruin T7 makes everything 4 power or less unable to block - and that's if you don't have any other creatures with counters on them. Also, a comment on the Ram: it got the correct community rating imo, but I saw a limited set review that claimed it's only good if you're running 7-8 gates and otherwise is bad. I think that's absurd. I'd be fine including it with half that amount in my deck. You only need a single gate in play for it to be fine, and two gates in play make it great. What else would you call a 4/4 vigilance trample for 3 mana?
2 on the cusp:
I like Titanic Brawl just fine, but it's got
Savage Smash as competition for fight spells and I'm choosing Smash if able. Mammoth Spider is a really good defensive piece against flyers in this set. I always want it in my sideboard, but sometimes my main deck will have better top end and spooder won't make my 40 cuts.
Honorable mentions:
Rampaging Rendhorn and
Saruli Caretaker. No, I don't think Caretaker is anywhere near the runnings for top 5, but I want to mention it in counter to how often I'm hearing it called garbage. It's ramp (if a bit awkward) that can help you out in a pinch or get your bomb out a turn sooner, but I think it's value as fixing is often overlooked. If I'm wanting to splash a 3rd color for off-color bomb and don't have gates to support it, I'm ok running this. Rendhorn is a vanilla 5/5 for 5, or a 5 mana hastey 4/4. Pretty decent for a common.
Multicolor to follow