Cheapest priced copy (Ravnica Remastered): $1.99 at Card Kingdom, near mint, their price list as of .
Aurelia, Exemplar of Justice 
Legendary Creature — Angel · 2/5 · Mythic · Guilds of Ravnica Promos · #153p
Flying
Mentor (Whenever this creature attacks, put a +1/+1 counter on target attacking creature with lesser power.)
At the beginning of combat on your turn, choose up to one target creature you control. Until end of turn, that creature gets +2/+0, gains trample if it's red, and gains vigilance if it's white.
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper
7 printings · $1.99 to $69.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Guilds of Ravnica | 153 | Mythic | $2.29 | $2.49 |
| Guilds of Ravnica Promos | 153p | Mythic | $5.99 | $14.99 |
| Guilds of Ravnica Promos | 153s | Mythic | — | $3.49 |
| Ravnica Remastered | 164 | Mythic | $2.29Out of stock | $2.49Out of stock |
| Ravnica Remastered | 356 | Mythic | $1.99 | $2.49 |
| Ravnica Remastered | 356z | Mythic | — | — |
| Ravnica Remastered | 436 | Mythic | $22.99 | $69.99 |
6 rulings from Wizards of the Coast
- 5 October 2018Mentor compares the power of the creature with mentor with that of the target creature at two different times: once as the triggered ability is put onto the stack, and once as the triggered ability resolves. If you wish to raise a creature’s power so its mentor ability can target a bigger creature, the last chance you have to do so is during the beginning of combat step.
- 5 October 2018If the creature with mentor leaves the battlefield with mentor on the stack, use its power as that creature last existed on the battlefield to determine whether the target creature has less power.
- 5 October 2018If the target creature’s power is no longer less than the attacking creature’s power as the ability resolves, mentor doesn’t add a +1/+1 counter. For example, if two 3/3 creatures with mentor attack and both mentor triggers target the same 2/2 creature, the first to resolve puts a +1/+1 counter on it and the second does nothing.
- 5 October 2018Aurelia’s last ability resolves before attackers are chosen.
- 5 October 2018The target creature gains trample and vigilance if it’s both red and white. It gets +2/+0 only once, even if it’s both red and white, and even if it’s neither red nor white.
- 5 October 2018Once Aurelia’s last ability has resolved, the creature keeps whatever bonuses it got from that ability even if its colors change.