Hi i couldn't find a ruling on riryoku so i was wondering...

does riryoku just halve/add the original atk? or just straight up atk... like with equips and such?

Unless a effect ask for Original ATK, anytime it states "ATK" only, it is taking into account all Modifiers, like Field Spell Cards (eg. A Legendary Ocean), Equip Cards (eg. United We Stand), and Monster Effects (eg. Star Boy).

So, if you had Gagagigo and Star Boy as your only monsters on the field with the above Modifiers, his ATK would be

ALO +200
United We Stand +1600
Star Boy +500

Gagagigo would have a whopping 4150 ATK. If your opponent played Riryoku on him, it would reduce Gagagigo to 2075, and add 2075 to whatever monster they targeted for the effect.

i see... thanks.

but u sure field effects are counted too? and after riryoku activates would the person the field card was on get back the field thing?

example: dark magician with yami on field (2700 atk)
someone uses riryoku , would that be 1350?
and if so after the enemies monster gets the 1350...
would dark magician go up to 1550? from yami again?

No, the monster would not get the field effect again, just like it doesn't get the boosts from other effects again. The boosts won't return until Riryoku's effect expires on the next turn.

alright thanks for clearing that up.