Although outclassed by Chansey and Blissey for a Normal-type tank, it has a pretty good niche as a Trick Room setter with its easily outclassed speed, however can outspeed some other Pokemon.
Porygon2
Role: Trick Room setter
252 HP, 252 DEF/SP.DEF
Ability: Analytic
Item: Eviolite
Tera Type: Ghost/Steel
Sassy/Relaxed nature
Recover (Good recovery if you want to stall.)
Trick Room
Tri Attack (pairs well with Analytic, STAB)
Thunder Wave/ Toxic (Thunder Wave cripples opponents, Toxic for stall.)
Another more offensive set:
Porygon2
Role: Bulky Special Sweeper
Item: Eviolite
Ability: Analytic
Tera Type: Ghost
Modest/Quiet nature
Tri Attack (great STAB, allows for extra status on opponents)
Ice Beam (makes for great coverage)
Psychic/Psyshock (coverage for those pesky Fighting types, Psyshock hits Chansey and Blissey better)
Recover (great healing)
Tera Steel is a great defensive typing, although keeping its Fighting weakness while sacrificing STAB for a better typing.
Tera Ghost removes its Fighting weakness, but sacrifices its STAB, again.