Bs blocker wont even take damage, and even in a low-trust situation they only have to risk their worst creature
There are two unusual cases where Narcomoeba's triggered is "delayed" so-to-speak letting you get additional Prized Amalgams into play before the Narcomoeba is returned to the battlefield
For example, if a creature has toxic 2 and gains toxic 1 due to another effect, combat damage that creature deals to a player will cause that player to get 3 poison counters
Most of the time, artwork, particularly for legendary creatures, depicts them casting some spell or doing something cool, not taking a midday nap
You can return it from the graveyard for free with Teshar, Ancestor's Apostle, and then sacrifice it to get another artifact back, which then triggers Teshar again, and so on
Colorless too