I believe the Wulfsbane you are referring to is the one between the two treasure nodes. If so he's 4018 I believe. And I guess you can do this grind on any node? Or is it better to do it on a treasure node?
Actually, nope! I'm speaking about the one on the opposite side, across from a weekend warrior, right after you fight the first two nodes of the NMO!
You can in fact grind on any node, but personally, I say the Wulfsbane or at the very least the single Weekend Warrior as you can then use one character until your energy runs out, switch, and do it again for another 3-4 tries!
Really the only reason to do a treasure node is on the first "reset" so to speak: AKA as soon as you start up the event. In theory, you can choose any node to fight and grind, but seeing as expert mode treasure nodes are rather tough AND you will only get 20% of the rewards you'd normally get (Just checked on the hints they display here and there!), you're better off simply grinding on a single fighter (weakest) of the event and pray to the RNG goddess herself that you receive a move you want.
Then, if you don't get it, wait till the next week and try again since the treasure nodes at least guarantee
a gold move be it a blockbuster or a special move.
I'd say a big thing about grinding, in general, is both patience and understanding because while we don't have an official word yet on the drop rates,
whatever they are gets reduced by 80% (meaning, for example, we normally get 600 coins by finishing one level. Replaying that level only rewards us 120 coins. Whatever % is the drop rate of a move then also gets reduced to the point that you have maybe a 20% chance of getting a move, besides a silver or bronze variation.) And that's just my own theory though, as after all, the game abides by RNG so it's all chance.
So, your best bet is simply grinding as often you can, hoping RNG works with you, beating treasure nodes and the event itself, or finding more gold Beowulf's (Not exactly everyone's option!) Like I said before, it takes patience, but eventually you'll get there to the point you need to! I had the best luck so far with Beo's moves, but try getting another move for Filia or Parasoul and my phone simply says "Nope."