Cheapest priced copy (Jumpstart 2022): $0.35 at Card Kingdom, near mint, their price list as of .
Chillerpillar 
Snow Creature — Insect · 3/3 · Common · Modern Horizons · #43
{4}{S}{S}: Monstrosity 2. (If this creature isn't monstrous, put two +1/+1 counters on it and it becomes monstrous. {S} can be paid with one mana from a snow source.)
As long as this creature is monstrous, it has flying.
Legal inCommanderModernLegacyVintagePauper
Not legal inBrawlStandardPioneer
2 printings · $0.35 to $0.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Jumpstart 2022 | 280 | Common | $0.35 | — |
| Modern Horizons | 43 | Common | $0.35 | $0.49 |
3 rulings from Wizards of the Coast
- 14 June 2019Chillerpillar gaining flying after it becomes blocked won’t remove the blocking creature from combat or cause Chillerpillar to become unblocked.
- 14 June 2019Monstrous isn’t an ability that a creature has. It’s just something true about that creature. If the creature stops being a creature, loses its abilities, or loses its +1/+1 counters, it will continue to be monstrous.
- 14 June 2019Once a creature becomes monstrous, it can’t become monstrous again. If the creature is already monstrous when the monstrosity ability resolves, nothing happens.