mtg cards you can have more than 4 of Varina, Lich Queen You gain that much life. All 'Any Number' Cards -

Life totals melt quickly, owing to the over-focus of modern creatures needing to attack or deal damage to trigger value based abilities

They work against mill in a similar fashion: Shuffling your library back into your deck against a mill deck is equivalent to resetting your life total to 20, 40, or whatever against a more standard Magic deck attacking your life total

I have definitely in the past cracked a Fetch at my opponents end step out of instinct, only to then draw a Fatal Push and not be able to kill my opponents creature as I wasted my Fetchland

I find the side-loading variety easier to insert cards into