Baldur’s status effect resists the same sort of enemies as before:
- Chao
- Li Xiu
- Leonidas
- Guinevere
- Neith
- Lady of the Lake’s Minions
etc — any enemy who directly reduces Mana.
The description update wasn’t a functional change, just terminology. Other Heroes with similar terminology were updated too in Version 28.
What did change in Version 28 is how Mana stealing works, though that’s unrelated to Baldur.