Cheapest priced copy (Guilds of Ravnica): $0.35 at Card Kingdom, near mint, their price list as of .
Ledev Champion 
Creature — Elf Knight · 2/2 · Uncommon · Guilds of Ravnica · #186
Whenever this creature attacks, you may tap any number of untapped creatures you control. This creature gets +1/+1 until end of turn for each creature tapped this way.
{3}{G}{W}: Create a 1/1 white Soldier creature token with lifelink.
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper
1 printing · $0.35 to $0.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Guilds of Ravnica | 186 | Uncommon | $0.35 | $0.49 |
4 rulings from Wizards of the Coast
- 5 October 2018You can tap creatures this way only as Ledev Champion's triggered ability is resolving. You can't tap more creatures later in combat to give it +1/+1 again.
- 5 October 2018Attacking creatures with vigilance may be tapped for Ledev Champion's first ability. If Ledev Champion itself has vigilance, it can be tapped this way, too. These creatures aren't removed from combat.
- 5 October 2018Creatures that have come under your control this turn can be tapped for Ledev Champion's first ability.
- 5 October 2018For Ledev Champion's first ability, the creatures to tap are chosen as the ability resolves. No player may take actions between the time you choose the creatures to tap and the time Ledev Champion's power and toughness are boosted.