Cheapest priced copy (Ravnica Allegiance): $2.49 at Card Kingdom, near mint, their price list as of .
Biomancer's Familiar 
Creature — Mutant · 2/2 · Rare · Ravnica Allegiance · #158
Activated abilities of creatures you control cost {2} less to activate. This effect can't reduce the mana in that cost to less than one mana.
{T}: The next time target creature adapts this turn, it adapts as though it had no +1/+1 counters on it.
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper
2 printings · $2.49 to $32.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Ravnica Allegiance Promos | 158s | Rare | — | $29.99 |
| Ravnica Allegiance | 158 | Rare | $2.49 | $32.99Out of stock |
4 rulings from Wizards of the Coast
- 25 January 2019Biomancer’s Familiar affects only abilities of creatures you control on the battlefield. The costs of activated abilities of creature cards that work in other zones (such as cycling) won’t be reduced.
- 25 January 2019Activated abilities contain a colon. They’re generally written “[Cost]: [Effect].” Some keyword abilities are activated abilities and will have colons in their reminder text. Triggered abilities (starting with “when,” “whenever,” or “at”) are unaffected by the cost reduction ability of Biomancer’s Familiar.
- 25 January 2019An ability that has only one generic mana and some amount of other mana symbols in its activation cost will have its cost reduced by {1}.
- 25 January 2019The last ability of Biomancer’s Familiar doesn’t add or remove any counters. It just lets the creature adapt despite already having +1/+1 counters on it.