Activate Antler Skulkin by paying {2}, giving Callous Sell-Sword persist until end of turn.
Activate Ashnod's Altar by sacrificing Callous Sell-Sword, adding {C}{C}.
When Callous Sell-Sword dies, its persist ability triggers, returning it from your graveyard to the battlefield with a -1/-1 counter on it.
Callous Sell-Sword enters the battlefield with an additional +1/+1 counter on it for each creature you controlled that died this turn.
Repeat.

Infinite +1/+1 counters on a creature

Infinite death triggers

Infinite ETB

Infinite LTB

Infinite sacrifice triggers

Antler Skulkin

Ashnod's Altar

Callous Sell-Sword // Burn Together

Painter's Servant

Cast Glamerdye by paying {1}{U}, changing all instances of "white" on Antler Skulkin to "black" until end of turn.
Activate Antler Skulkin by paying {2}, giving Callous Sell-Sword persist until end of turn.
Activate Ashnod's Altar by sacrificing Callous Sell-Sword, adding {C}{C}.
When Callous Sell-Sword dies, its persist ability triggers, returning it from your graveyard to the battlefield with a -1/-1 counter on it.
Callous Sell-Sword enters the battlefield with an additional +1/+1 counter on it for each creature you controlled that died this turn.
Repeat from step 2.

Glamerdye

Cast Trait Doctoring by paying {U}, changing all instances of "white" on Antler Skulkin to "black" until end of turn.
Activate Antler Skulkin by paying {2}, giving Callous Sell-Sword persist until end of turn.
Activate Ashnod's Altar by sacrificing Callous Sell-Sword, adding {C}{C}.
When Callous Sell-Sword dies, its persist ability triggers, returning it from your graveyard to the battlefield with a -1/-1 counter on it.
Callous Sell-Sword enters the battlefield with an additional +1/+1 counter on it for each creature you controlled that died this turn.
Repeat from step 2.

Trait Doctoring

Cast Whim of Volrath by paying {U}, changing all instances of "white" on Antler Skulkin to "black" until end of turn.
Activate Antler Skulkin by paying {2}, giving Callous Sell-Sword persist until end of turn.
Activate Ashnod's Altar by sacrificing Callous Sell-Sword, adding {C}{C}.
When Callous Sell-Sword dies, its persist ability triggers, returning it from your graveyard to the battlefield with a -1/-1 counter on it.
Callous Sell-Sword enters the battlefield with an additional +1/+1 counter on it for each creature you controlled that died this turn.
Repeat from step 2.

Combos with "Callous Sell-Sword // Burn Together"