GURPS is a realistic, generic system.
200 Character Points is a reasonable level for PC-quality federal agents.
Allies: The other PC's are NOT Allies. Friendlies may be Allies, or Contacts.
Detect: Some people are naturally sensitive to manifestations of the Mythos. Tragically, those with he ability to sense Mythos manifestations are often the kind of people least capable of dealing with them. The GM may restrict this advantage to artist, addicts and the insane.
Fearlessness: Consult with your GM on whether or not this advantage will help you in confronting the Mythos. In any case, don't overdo it.
Magery: Mythos forces have nothing to do with the manipulation of "Mana". Magery is not required to cast Mythos spells.
Patron: Delta Green (Fairly power organization, special abilitis +50%, quite often) 30 points.
True Faith: Your average Mythos critter will not be terribly impressed by a crucifix.
Unfazeable: This advantage is disallowed. Or, it gives you a basic Fright Check of 14 or less, and you automaticaly pass all Fright Checks that aren't Mythos-related.
Addiction, Alcoholism, Bad Temper, Berserk, Chronic Depression, Delusions, Fearfulness, FLashbacks, Guilt Complex, Insomniac, Loner, Low Empathy, Nightmares, Obsession, On the Edge, Paranoia, Phantom Voices, Phobias, Sleepwalker, Split Personality, Stuttering: These disadvantages are common symptoms of sanity loss.
Combat Paralysis, Cowardice, Curios: These disadvantages are best suited for agents who don't do a lot of field work.
Duty: To Delta Green, fairly often, Extremely Hazardous. -15 points.
Enemies: Operatives rarely have enemies. They might acquire them during the campign, however.
Secret: Being a Delta Green member is a -20 points secret.
Weirdness Magnet, Xenophilia: These disadvantages are ''dangerous''.
Original disclaimer: ''The material presented here is my original creation, intended for use with the GURPS system from Steve Jackson Games. This material is not official and is not endorsed by Steve Jackson Games.''