The deal just started a few minutes ago, but seems like their Mastercard promotion stacks with the existing BOGO 50% off sale. Use coupon code MC25 to receive an additional $25 off $150. Although the modulars and online exclusive sets are excluded from the BOGO deal, it works with the Mastercard promotion. Thanks to forum member sidersdd for the heads up.
Stack it with the $10 Groupon for $20 Worth of Toys at Toys R Us and you can possibly score a deal with their BOGO 50% off sale (assuming you buy sets that are at MSRP or on sale, which there aren’t many unfortunately).