Pot-limit Omaha where a die roll after the flop decides if the pot splits at all.
Button and blinds.
Four hole cards, a flop, a die roll, then the turn and river.
Small bet preflop and on the flop, big bet on the turn and river.
Half the possible rolls turn it into a straight high-only pot; the other half turn it into an 8-or-better hi/lo split. You don't know which you're playing until the die lands.