Pre-listen Card Critique: Herald of Thorns
I love a good french vanilla, especially as a way of showcasing a new mechanic. Savage is the kind of mechanic that definitely belongs at common, and in green. Without knowing any further context, it seems like it would be most at home in a Naya shard. Savage makes blocking more complicated for a competitive opponent. It makes combat exciting for newer players that are more focused on exploring the game than on learning strategy. The scaling factor it presents means opponents have high incentive to trade creatures and keep the board clear, but Savage itself makes it harder to trade. There's cool play there, which makes this a mechanic I'd be very interested in playing with. There's definitely room for more flavor here, and that's where the card is most in need - a great sign. The only mechanical caveat I'd point out is that for a common that can get P/T shifts intrinsically, you're best off using square stats and you're best off using single colored mana costs. So, in essence, I guess I'm suggesting this card be a Hill Giant with Savage instead of Balduvian Barbarians. Overall I'd give this a 7, an 8 with any reasonable flavor text, and 8.5 with those small tweaks. I dig it!
Savage looks like a pretty sub par mechanic to me. It only triggers when it becomes blocked, and then only if I have other attacking creatures? Blocking usually isn't a priority unless you're close to death too. It's not quite as narrow as rampage, but it certainly approaches that. I'm not sold on the flavor of getting bigger because you have other attacks as "savage" either. I'd expect a savage to be savage regardless of other attackers.
Savage is fairly bad evasion. I mean, it's no bushido; in fact it's almost literally a Fumiko the Lowblood ability downgraded in several ways. Like Icarii said, it's just barely a better version of rampage. You're getting somewhere as far as evergreen space, but this is not the right execution.
Mutate is compelling in gameplay but sort of baffling in flavor. Why does it go from the graveyard? Reflavored I would expect a name like "throwback" or similar to imply an extinct species coming back, and then put it in a dinosaur-themed set.
I think the main problem with savage is that it is smooshing together two actually separate unrelated things. Attacking with lots of creatures pumps the creature so it deals more damage would be good. Blocking the creature pumps it so it can be harder to kill and can kill more of its blockers would be good. Except with savage you need to do both at the same time. It feels like it wants to be something like either Aurochs or Elvish Berserker, but is instead an awkward unplayable mix.