Arcane Ammo. The sniper infuses their magic directly into their ammunition and inscribes spells on the stock of their weapon. Whenever they attack, the DM can declare that a spell bullet is loaded in the chamber. In response, players may drop to the ground to grant the attack disadvantage. If the attack hits, the player must make a saving throw or suffer the effects of the spell. The wizard may choose to forgo dealing damage with the attack itself to impose disadvantage on that saving throw. 

Spellcasting. The Zauberschutze is a 8th-level spellcaster. Its spellcasting ability is intelligence (spell save DC 16, +6 to hit with spell attacks). The Zauberschutze has following wizard spells prepared. When the Zauberschutze loads an Arcane Ammo, they choose from one of their prepared spells and lose a spell slot of appropriate level:
Cantrips (at will): message, mold earth, dancing lights, prestidigitation
1st level (4 slots): chromatic orb, ice knife, sleep, thunderwave
2nd level (3 slots): blindness/deafness, mind spike, tasha's mind whip
3rd level (3 slots): fireball, slow, dispel magic
4th level (2 slots): banishment

The Long Game. Sniper wizards consume alchemical tinctures to delay natural death and slow their metabolism to a snail's crawl, slowing their heartbeats and entering a trance-like state of overwatch over an area. They can maintain this state for years, ready to pull the trigger on any target within 1 mile of their vantage point. Any creature hit by an attack while the wizard is in this trance automatically fails any saving throws against spell bullets caused by the attack. After making an attack in this way, the trance ends.

Hexenjager. Ranged Weapon Attack: +7 to hit, range 1,200 ft., 1 target. Hit: 11 (1d12 + 4) force damage. If the attack roll scores a critical hit, the target of that missile takes 26 (4d12) force damage instead of you rolling damage twice for a critical hit. 

Aether Extraction. When a creature ends its turn within melee range of the sniper, as a reaction roll a d4. On a 1, they teleport up to 250 feet away in any direction to gain some cover and a vantage point.