Help with making a homing entity which despawns after 1 hit

Hello Im trying to make a AI to achieve to following:

The mob will be always stationary when it detects a mob it can reach (the mob is flying)
It will go after it
but not the following: villagers, animals, players, golems
(so hostile mobs only)
and when it hits once it will despawn

(If its remained stationary and cant find a target it will despawn in 5 seconds

can someone tell me how can I do it in a detailed way?

Im not sure how to exactly implement the despawn if stationary. I am also open to suggestin in change of how it works.

Thanks