The round kicked off on Wednesday with two Welsh festive derbies - the second-placed Scarlets lost 32-3 to the Ospreys in Swansea, as the reigning champions stepped up their challenge for back-to-back titles.
The result sent the Ospreys up to fifth in the standings just outside the play-off zone, with their rescheduled round 11 fixture against the Newport Gwent Dragons to come on New Year's Eve.
In Wednesday's other all-Welsh tie, home advantage helped the Cardiff Blues end a run of disappointing defeats as they edged out the Dragons on a 12-10 scoreline.
Two of the four games on Saturday will decide the end-of-year 'pecking order' in both Scotland and Italy, as the return legs of the double header between Benetton Treviso and Zebre and Edinburgh and Glasgow Warriors take place.
The Warriors currently hold the upper hand in Scoltand, as do Treviso in Italy having already taken an away victory last week.
The final match of the round is at the RDS on Saturday evening where Leinster will be anxious to maintain their unbeaten home record and improve their standing in the table at the expense of familiar opponents Connacht.
RABODIRECT PRO12 - ROUND 12 RESULTS/FIXTURES:
Wednesday, December 26 -
Cardiff Blues 12 Newport Gwent Dragons 10, Cardiff Arms Park
Ospreys 32 Scarlets 3, Liberty Stadium
Saturday, December 29 -
Benetton Treviso (8th) v Zebre (12th), Stadio di Monigo, 3pm local time (live SportItalia)
Edinburgh (9th) v Glasgow Warriors (4th), Murrayfield, 4.05pm (live BBC ALBA)
MUNSTER (3rd) v ULSTER (1st), Thomond Park, 5.30pm (live RTÉ Two/BBC 2 Northern Ireland)
LEINSTER (6th) v CONNACHT (10th), the RDS, 7.45pm (live TG4)