Fountain offers a massive reward for only needing three Copper above the starting total. It's trivial in Mountebank games, fairly easy in an engine with lots of +buy eg Workers Village, and Beggar does it easily too. It's more interesting in money games. If you only have one buy, then you obviously need to pick up those coppers - they're worth a whopping 5VP each. The question is when do you get them? Additionally, if there's copper trashing on the board, do you skip it, or can your thin deck outscore someone going for 10 coppers?
Battlefield offers an additional 12VP for the first few green cards built. I can see this not being a huge deal in many games - perhaps you'll start greening a little earlier and split the VP 8-4. Or, as Donald X mentions, pick up an Estate and trash it. It's pretty cool for alt-VP strategies, where you aggressively buy out e.g. the Gardens early. It's also a nice little bonus for gaining Great Hall or Island.
Wolf Den will hurt some engines. You want to add a second copy of any of your payload actions, most likely. This might just reduce diversity (and result in things like double Militia), or increase terminal collision. Maybe you could buy it in the last couple of turns. It affects Duchy dancing. That first Duchy isn't worth any VPs, so you need to get that second one to counterbalance it. It also interacts with a lot of cards. Golden decks are going to be undesirable, looters and Swindler get a boost, and Black Market/Tournament/Knights might be skippable with Wolf Den out.
Tomb mostly looks like a little buff to any trashing on the table. It also gives something to do in the lategame - start trashing cards out of your deck for a bit of extra VP when the game is close to the end. It also makes you feel better about trashing the starting Estates - no need to keep one around as a tiebreaker.
Keep is going to be a huge BM card. BM decks are trivially going to pick up at least 10 VP from this card against an engine. In the BM mirror, it will encourage continuing to build - Golds are the obvious fight you want to win, and you might need to ignore Provinces for a while to do it. Fun with any kingdom treasures which are out. Cache is now a card you need to win the split on.