Help with Stalker Entity

Heya! So ive been working on a mod, and one of my mobs is a Stalker-like entity

To clarify what that means in this case, they

• Will vanish/become shortly after the player either looks at them or doesn't notice them for too long, and keep reappearing, closer and closer to the player
• Once the mob reaches the player, it will attack and will vanish once taken about 10 damage, restarting the cycle of sneaking back up on the player

Any help on figuring out how to do this is appreciated! I can clarify on anything if needed

(Yes the mob is based off the Creaking)