Some monster math games include "Math Monster Multiplication" and "Math Monster Addition." Both of these gamers are free to play at MathPlayground.com, as of 2016.
In "Math Monster Multiplication," players select the numbers they want in their multiplication questions. Next, they enter the scary door to play. Players see one multiplication problem with four possible answers. For each question, a new monster appears around the problem. When the corrected answer is selected, the monsters spin.
"Math Monster Addition" offers addition questions with numbers zero to 10, and the player chooses the numbers that are allowable. Each time a question is answered, a new monster appears. When all the monster spaces are filled, the players see the percentage of addition problems that they got correct.