Cheapest priced copy (Guildpact): $0.35 at Card Kingdom, near mint, their price list as of .
Aetherplasm 
Creature — Illusion · 1/1 · Uncommon · Ravnica Remastered · #34
Whenever this creature blocks a creature, you may return this creature to its owner's hand. If you do, you may put a creature card from your hand onto the battlefield blocking that creature.
Legal inCommanderModernLegacyVintage
Not legal inBrawlStandardPioneerPauper
2 printings · $0.35 to $0.79 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Guildpact | 22 | Uncommon | $0.35 | $0.79 |
| Ravnica Remastered | 34 | Uncommon | $0.35 | $0.49 |
5 rulings from Wizards of the Coast
- 1 February 2006If you want, you can return Aetherplasm to your hand and not put anything onto the battlefield. The attacking creature will still be considered blocked, so it won't be able to deal combat damage to you unless it has trample or a similar ability.
- 1 February 2006Aetherplasm will return to your hand before any combat damage is assigned.
- 1 February 2006The creature you put onto the battlefield from your hand is blocking the attacking creature, even if the block couldn't legally be declared (for example, if that creature enters tapped, or it can't block, or the attacking creature has protection from it).
- 1 February 2006The creature you put onto the battlefield may be the Aetherplasm you just returned to your hand. This allows it to dodge abilities like Deathgazer's.
- 12 January 2024Although the creature that enters the battlefield is blocking, it was never declared as a blocking creature for the purposes of abilities that trigger whenever a creature blocks (such as Aetherplasm's ability, for example).