Colonel Autumn

• WOTC Official Reminder Textofficial rules
  Lifelink — Damage dealt by this creature also causes you to gain that much life.

• WWizards of the Coast2024-03-08
  Official Ruling
  You can sacrifice the creature with exploit if it’s still on the battlefield. If it has an ability that triggers when it exploits a creature (or, in this case, when any creature you control exploits a creature), that ability will trigger.
• WWizards of the Coast2024-03-08
  Official Ruling
  You choose whether to sacrifice a creature and which creature to sacrifice as an exploit ability resolves.
• WWizards of the Coast2024-03-08
  Official Ruling
  If Colonel Autumn isn’t on the battlefield as an exploit ability of a creature you control resolves, Colonel Autumn’s last ability won’t trigger. You won’t get +1/+1 counters, even if you sacrifice a creature.
• WWizards of the Coast2024-03-08
  Official Ruling
  You can’t sacrifice more than one creature to any one exploit ability.
• WWizards of the Coast2024-03-08
  Official Ruling
  A creature with exploit “exploits a creature” when the controller of an exploit ability sacrifices a creature as that ability resolves.

Rulings via Scryfall