What does Boyars do in AoE3?

Cavalry Archer: hit points +10%, damage +10%; Cossack: hit points +10%, damage +10%; Veteran Oprichnik: hit points +10%, damage +10%. The game says: "Cavalry Archer, Cossack and Oprichnik attack and hitpoints increased."

Home City card

Boyars

Boyars (tech ID HCUniqueCombatRussian) is a Home City card in AoE3: Definitive Edition 100.19.18309, in the decks of 1 civilization, sent from the Colonial Age. Effect: Cavalry Archer: hit points +10%, damage +10%; Cossack: hit points +10%, damage +10%; Veteran Oprichnik: hit points +10%, damage +10%.

Quick answers (3)

Which civilizations have the Boyars card?: Russians.
What does Boyars do in AoE3?: Cavalry Archer: hit points +10%, damage +10%; Cossack: hit points +10%, damage +10%; Veteran Oprichnik: hit points +10%, damage +10%. The game says: "Cavalry Archer, Cossack and Oprichnik attack and hitpoints increased."
What is the tech ID of Boyars?: HCUniqueCombatRussian.

Cavalry Archer, Cossack and Oprichnik attack and hitpoints increased.

What it does

Cavalry Archer: hit points +10%, damage +10%
Cossack: hit points +10%, damage +10%
Veteran Oprichnik: hit points +10%, damage +10%

Cost: 1
Sent from: II
Times it can be sent: 1
Game ID: HCUniqueCombatRussian

In these decks

RussiansII×1

Source: techtreey.xml and the Home City files, AoE3: DE 100.19.18309 (build 25040513).