Umm... Water/Psychic and Grass/Psychic weren't new type combos.
Water/Psychic: Slowpoke, Slowbro, Starmie
Grass/Psychic: Exeggcute, Exeggutor
New Types Introduced in Gen II:
Dark
Steel
New Type Combo's Introduced in Gen II:
Key:
Primary Type/Secondary Type if any (Pokemon with Type Combo)
Dark (Umbreon)
Dark/Fire (Houndour/Houndoom)
Dark/Flying (Murkrow)
Dark/Ice (Sneasel)
Steel/Ground (Steelix)
Steel/Flying (Skarmory)
Normal/Psychic (Girafarig)
Fire/Rock (Magcargo)
Rock (Sudowoodo)
Rock/Dark (Tyranitar)
Ground/Flying (Gligar)
Electric/Steel (Magnemite/Magneton)*
Bug/Steel (Forretress, Scizor)
Bug/Fighting (Heracross)
Bug/Rock (Shuckle)
Grass/Flying (Hoppip/Skiploom/Jumpluff)
Ice/Ground (Swinub/Piloswine)
Water/Dragon (Kingdra)
Water/Ground (Wooper/Quagsire)
Water/Electric (Chinchou/Lanturn)
Psychic/Flying (Natu/Xatu, Lugia)
Ghost (Misdreavus)
*Magnemite and Magneton were pure Electric in RGBY, so Electric/Steel was indeed a new type combo, even though it belonged solely to Pokemon introduced in Generation I.