help with custom mob behavior

i am trying to make a mob that, upon noticing the player or a mob it is hostile to:

1. saves its targets position
2. waits for 1 second
3. moves towards saved position with increased speed and dies when reaching it (mob explodes on death, i already have that part made)

i have no idea on how to change mob behavior beyond the provided task/goals editor, so general information on the tools to do this for the future will be greatly appreciated