My hand has a fully powered, disabled Murder ready to go.
AI has a 20/20 Resplendent Angel in the first slot, 7/7 Lyra Dawnbringer in the second.
Attack phase commences, I cast the murder as normal, killing (temporarily) the RA. It goes to 0 toughness, and does not attack. Lyra hits for seven, triggering the ability of a creature that’s already supposed to be dead, reinforcing the RA. Since the RA can now attack, having 5 toughness from the reinforcement, it does so, hitting for 25 lifelink and reinforcing itself again.
Triggered abilities of dead creatuees SHOULD NOT BE TRIGGERING. WE’VE BEEN OVER THIS, DEVS.
This doesn’t sound like an issue with Murder as much as the ongoing debate/effects of the programmatic decision to not officially kill creatures until after combat has completely ended.
@Tombstone This also happens with Vraska’s Pirate tokens/support from her 2nd loyalty ability. I had a deathtouch creature (Ochran Assassin) attack the pirates which took them to 0 toughness, and then the support triggered and the dead pirates managed to explore in their not-living state to get +1/+1 and not leave the battlefield. While this exhibits the same issue as the OP had, it also shows that the game is not handling the assured destruction of Deathtouch.
Edit: I also had Forebear’s Sword out so the assassin had trample which made excess damage go to Vraska, though I’m pretty sure I’ve seen overkill damage still not cover the +/+ effects after the attack happens, and also shouldn’t have bearing on the deathtouch.
It seems as it may be connected to the flash ability of the spell not registering to kill the creature until after combat. I’ve observed similar issues when using Ultimate Price to kill an attacking creature.
I’d have to test it out, but I’m willing to bet Inescapable Blaze and Necrotic Wound all would share the same type of issue.