Cheapest priced copy (Final Fantasy Commander): $0.49 at Card Kingdom, near mint, their price list as of .
Maester Seymour 
Legendary Creature — Human Elf Cleric · 1/3 · Rare · Final Fantasy Commander · #160
At the beginning of combat on your turn, put a number of +1/+1 counters equal to Maester Seymour's power on another target creature you control.
{3}{G}{G}: Monstrosity X, where X is the number of counters among creatures you control. (If this creature isn't monstrous, put X +1/+1 counters on it and it becomes monstrous.)
Legal inCommanderLegacyVintage
Not legal inBrawlStandardPioneerModernPauper
2 printings · $0.49 to $8.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Final Fantasy Commander | 68 | Rare | $0.49 | $1.99 |
| Final Fantasy Commander | 160 | Rare | $1.79 | $8.99 |
4 rulings from Wizards of the Coast
- 6 June 2025The value of X is determined only once, as Maester Seymour's last ability resolves.
- 6 June 2025Once a creature becomes monstrous, it can't become monstrous again. If the creature is already monstrous when the monstrosity ability resolves, nothing happens.
- 6 June 2025If Maester Seymour is no longer on the battlefield when its first ability resolves, use its power as it last existed on the battlefield to determine how many +1/+1 counters to put on the target creature.
- 6 June 2025Monstrous isn't an ability that a creature has. It's just something true about that creature. If the creature stops being a creature or loses its abilities, it will continue to be monstrous.