Wilderlands: The Rise of Tharizdun
I’m not big on house rules, but some rules in 5e are vague, so I’d like to get ahead of them.
A creature must be undetected by all members of the opposing group to get a surprise round. A creature detected by at least one member of the opposing group still gains advantage on attacks, as normal.
Area of Effect
[update] if the effect crosses the square (even a little bit), then the creature is affected.
Technically, there is no resisting forced movement (RAW), but this can lead to some anti-climactic encounters. In the case of forced movement into severely hazardous terrain (eg. into a lava flow or off a high cliff), creatures can save (dex 10) to be prone, and dangling / windmilling just over the hazard. As an action, the creature can make a check (dex/str 15) to move back to safety, and a move action to get out of the prone position. Another creature can move within reach, and make the check as an action as well. DM decides where this is applicable, but in-general a hazzard that does party level x 2 dice of damage would qualify; a twenty-foot drop (2d6) off a roof would not qualify for a 6th level party, but a 120-foot fall off a cliff (12d6 damage) would.