Strange. But comparing to Ajani's Mantra, this is very weak.

I don't mind weak cards. I just don't like them to be conditional/hard-to-earn life gain that doesn't pay off because people seem to hate those.

Ditch the threshold and it's probably still reasonable. It doesn't do anything else, it's only opponents, which balances it against the various 'whenever someone casts an artifact' type of cards. It's verra nice in multiplayer, though. But it's still slow and conditional lifegain; it's never going to be superpowered.

I assume this was meant as a reference to Hunting Grounds. Perhaps the "may gain 1 life" should be something like "may gain 3 life".