Legendary Planeswalker — Grist
As long as Grist isn't on the battlefield, it's a 1/1 Insect creature in addition to its other types.
+1 : Create a 1/1 black and green Insect creature token, then mill a card. If an Insect card was milled this way, put a loyalty counter on Grist and repeat this process.
−2 : You may sacrifice a creature. When you do, destroy target creature or planeswalker.
−5 : Each opponent loses life equal to the number of creature cards in your graveyard.
If Grist is no longer on the battlefield as its first loyalty ability resolves, you will still create a 1/1 black and green Insect creature token and mill a card. If an Insect card is milled this way, you won't be able to put a loyalty counter on Grist, but you will still repeat the process. More mill for the Grist, as it were.