Cheapest priced copy (Chronicles): $0.49 at Card Kingdom, near mint, their price list as of .
Sentinel 
Artifact Creature — Shapeshifter · 1/1 · Rare · Legends · #294
{0}: This creature's base toughness becomes equal to 1 plus the power of target creature blocking or blocked by this creature. (This effect lasts indefinitely.)
Legal inCommanderLegacyVintage
Not legal inBrawlStandardPioneerModernPauper
3 printings · $0.49 to $11.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Chronicles Foreign Black Border | 107 | Rare | — | — |
| Chronicles | 107 | Rare | $0.49 | — |
| Legends | 294 | Rare | $11.99 | — |
One ruling from Wizards of the Coast
- 1 October 2009You apply power/toughness changing effects in a series of sublayers in the following order: (a) effects from characteristic-defining abilities; (b) effects that set power and/or toughness to a specific number or value; (c) effects that modify power and/or toughness but don’t set power and/or toughness to a specific number or value; (d) changes from counters; (e) effects that switch a creature’s power and toughness. This card’s effect is always applied in (b), which means that effects applied in sublayer (c), (d), or (e) will not be overwritten; they will be applied to the new value.