Cheapest priced copy (Weatherlight): $1.49 at Card Kingdom, near mint, their price list as of .
Mwonvuli Ooze 
Creature — Ooze · 1+*/1+* · Rare · Weatherlight · #135
Cumulative upkeep {2} (At the beginning of your upkeep, put an age counter on this permanent, then sacrifice it unless you pay {2} for each age counter on it.)
Mwonvuli Ooze's power and toughness are each equal to 1 plus twice the number of age counters on it.
Legal inCommanderLegacyVintage
Not legal inBrawlStandardPioneerModernPauper
1 printing · $1.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Weatherlight | 135 | Rare | $1.49 | — |
2 rulings from Wizards of the Coast
- 4 October 2004Its power/toughness changes when the cumulative upkeep resolves, not when it triggers.
- 1 April 2008If you choose not to pay Mwonvuli Ooze’s cumulative upkeep, it will still get an age counter before being sacrificed. Its power and toughness will momentarily increase before being put into the graveyard, which might matter to certain other cards (such as Proper Burial).