Whenever a creature an opponent controls dies, put a +1/+1 counter on Yahenni.
Sacrifice another creature: Yahenni gains indestructible until end of turn.
Yahenni is a mono-black aristocrats commander that grows off opponents' creatures dying while functioning as a free sacrifice outlet that protects itself. You build a board of token generators and death-trigger payoffs, sacrifice creatures repeatedly to drain the table and feed value, and either grow Yahenni into a lethal evasive threat or assemble a sacrifice combo to win.
Free, repeatable sac outlet on the command zone with built-in indestructibility for protection
Haste lets it pressure or block immediately and dodge sorcery-speed removal via its own ability
Mono-black gives access to elite tutors, recursion, and ramp consistency
Scales naturally in grindy multiplayer games and during board wipes
Only one color means no access to enchantment removal and limited flexibility
Yahenni's own counters do nothing without evasion or trample to close games
Relies on a steady supply of creatures to sacrifice; runs dry against efficient creature removal
Vulnerable to exile-based removal and graveyard hate that shuts down recursion