Find the item that breaks the pattern, but don't stop at seeing it; you have to pin down exactly which rule it violates, and subtler breaks score more.
A board of shapes varies by colour, fill, form and a hidden numeric value. One or more of them break a rule the others all follow. Select an item, then tag which rule it breaks from the list. Correct calls reveal the rule; tag every broken rule to finish the round. The more obscure the rule, the bigger the payoff.
Oddity is an odd-one-out reasoning test that demands you justify the answer by naming the rule, deepening classification skills.
Finding the item that breaks a rule the others follow is the odd-one-out, a staple of reasoning assessment, and it rests on concept learning: you cannot spot the exception until you have induced the regularity.
The original requirement is that you name the rule broken, not merely point at the outlier.
That closes the genre's usual loophole. In a plain odd-one-out several answers can be defended, because almost any item differs from the rest in some respect; demanding the specific rule makes the answer checkable, and rewarding obscure rules pushes you past the first difference you notice.
Oddity is an original free browser take on the odd-one-out reasoning test, demanding you justify the answer by naming the broken rule. Built in-house for PlayPendium.