Cheapest priced copy (Mirrodin Besieged): $0.69 at Card Kingdom, near mint, their price list as of .
Cryptoplasm 
Creature — Shapeshifter · 2/2 · Rare · Mirrodin Besieged · #23
At the beginning of your upkeep, you may have this creature become a copy of another target creature, except it has this ability.
Legal inCommanderModernLegacyVintage
Not legal inBrawlStandardPioneerPauper
1 printing · $0.69 to $2.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Mirrodin Besieged | 23 | Rare | $0.69 | $2.99 |
4 rulings from Wizards of the Coast
- 1 June 2011If another creature becomes a copy of Cryptoplasm, it will become a copy of whatever Cryptoplasm is currently copying (if anything), plus it will have Cryptoplasm’s triggered ability.
- 1 June 2011If the creature is an illegal target when the ability tries to resolve, it won’t resolve. Cryptoplasm won’t become a copy of that creature; it remains whatever it was before.
- 1 June 2011The copy effect lasts indefinitely. Often, it will last until it is overwritten by another copy effect (if it copies another creature on a future turn, perhaps.)
- 1 June 2011You choose the target for the triggered ability when the ability is put onto the stack. You choose whether or not Cryptoplasm becomes a copy of that creature when the ability resolves.