Liliana of the Veil is best paired with a strategy to make use of all that discard , such as reanimation or delirium, but even if you don't, getting Liliana of the Veil to six loyalty counters isn't very hard to do, and it's devastating to an opponent
They were made to support the magecraft mechanic, so cards with magecraft and prowess are a good fit
While Snorlax Stall relies on its slow playstyle to do much of the heavy lifting, Froslass/Venomoth relies heavily on its Ace Spec card to win matches
You only ever play See Beyond if you have a specific need to do this in your deck, perhaps something like a Tinker deck
getting 6-9 mana for an investment of three mana is the bit that most decks are interested in
You can activate one ability of a planeswalker you control once a turn, but only during a main phase when you would cast a sorcery