Different Cultivation

Tin, Iron, Copper, Platinum, Bronze, Silver, Gold, Vibranium, Adamantine, Uru stages.

For people that want their MCs to be OP OP but not Golden Superman, Saitama, Rune King Thor with Thorforce Op level.

You could even make it so this cultivation is a transformation too and uses stamina and/or chi. The higher the level, the more control the user has over their transformation (e.g. at Tin level, user can only do a full body transformation like Osmosians from Ben 10 that absorb matter and look like a walking pile of what they touched, best example being Kevin in Ben 10 alien force, ultimate alien and omniverse. Also the amount of stamina/chi being exhausted is alot. Then they reach Silver level and gain partial-shift/transformation ability to make it where they don't need to do a full body transformation everytime, only transforming a part of their own body or limbs into the metals saving stamina/chi for future use.). Think of it like Armament Haki except with different colors based on the different metals (e.g. Gold will be yellowish etc. you get it).

It's a ten level body cultivation with seven ordinary levels starting with Tin level working your way up to Gold level and three mystical levels from Vibranium to Uru.

With every increase in cultivation and unlocking of a new ordinary transformation, the base level body gets an increase in strength. (Tin level is human level strength, unlocking iron transformation gives the user the strength of two adults. Copper form gives three. Platinum four. Bronze five, Silver six and Gold seven people in one.) Transforming doubles that strength (tin form gives the strength of two adults, Iron gives four. Copper six, Platinum eight, Bronze ten, Silver twelve, and Gold fourteen adults).

Only when unlocking the mystical transformations does the users strength dramatically increase without the need for transforming. Unlocking Vibranium stage triples strength giving the user strength of twenty one adults (transformation gives strength of sixty three adults). Adamantine triples that giving the user strength of sixty three adults (while transformed, 189 adults in one) and Uru triples giving the strength of 189 adults (and while transformed gives strength of 567 adults in one.)

An high level person e.g. Uru level person with strength of 189 adults can still use lower level ordinary transformations but no matter what they are (whether Tin, or Gold), they'll only double their strength giving them the strength of 378 adults. Only the mystical transformations triple strength.

Think of the adult used in this setting as Bruce Batman Wayne. He can lift approximately one ton with difficulty and push 2.5 tons with his feet when he's back is to the ground.

Based on the one ton limit used in this case to refer to an adult,.. then reaching Iron level lets the user lift two tons more. Copper three tons. Platinum four tons. Bronze five tons, Silver six tons, Gold seven tons, Vibranium twenty one tons, Adamantine sixty three tons and Uru 189 tons.

When transformed, in Tin form, the user can lift max two tons. In Iron form, max four tons. Copper form, six tons. Platinum form, eight tons. Bronze form, ten tons. Silver form, twelve tons. Gold form, fourteen tons. Vibranium form, sixty three tons. Adamantine form, 189 tons. Uru form let's user lift 567 tons.

The mystical transformations don't just give a great boost in strength passively without transforming and actively (through transformation) but come with their own abilities that makes them mystical transformations.

Vibranium transformation once unlocked gives kinetic energy absorbtion and manipulation and the ability to sense and see people through vibrations like Toph Beifong from Avatar Last Airbender. User becomes sensitive to vibrations that he/she can passively sense some movements made when they're loud enough to learn what direction they're from.

Adamantine transformation gives user ability to control body. Make or turn their limbs and body into objects, weapons e.g. could turn their hands into blades to cut stuff, could make their transformed fingers keys to break into a place, make their hand into a huge hammer to smash stuff. Also their durability is passively enhanced to high levels.

Uru transformation when unlocked let's user sense universal and dimensional energies and even access them, absorb, store, control, manipulate, convert/transform them.

Because of this system, they do have a limit they can eventually reach. And it makes them OP but not strength wise with Hulk and Thor that can 900+ tons.

Of course things can be different if for example the human standard their adult strength is based on is a superhuman like Captain America with his Five tons as the beginning or Spiderman with his twenty five tons as a base and not a normal human like Bruce Wayne because the cultivation is separate from Super Soldier Serums, Oz Serums, spider bites etc. MC could be Spiderman with strength of 25 tons in the beginning and reaches Iron level and as a result lifts 26 tons, Copper 27 tons, etc.