Teferi’s Curse is an interesting card. Phasing was a confusing mechanic for many, particularly for newer players. It removes things from play but doesn’t trigger “leaves play” or “comes into play” triggers. The card simply ceases to exist when it is phased out. It’s handy when you can control it, like Mist Dragon, but having your creature phase out is otherwise difficult to take advantage of except in narrow situations.
I also have to wonder why they limited Teferi’s Curse to only artifacts and creatures. Why not enchantments? I can see why they didn’t want to give land phasing as pseudo-land removal for blue would be quite out of color. If they had worded this as “non-land permanents” then it might find a home in casual decks trying to reset their planeswalkers, but of course this card was printed years before planeswalkers existed.
Quagmire Lamprey has something akin to Wither but only when he’s attacking (and of course he came along years before Shadowmoor). It’s odd to me that he’s a Fish. In fact, Quagmire Lamprey is the only black Fish in Magic (not counting Changelings). Fish has been a decidedly blue creature type since the early days of Magic (such as Dandan and Devouring Deep). The ability is black but the creature type definitely is not.
I don’t think either of these cards would ever see print in a modern set. They’re confusing, which Wizards’ doesn’t like, and they don’t pay off that confusion with interesting play choices or powerful effects.