Focused Practiser (5e Feat)
From D&D Wiki
Focused on self-improvement in one area, you have trained yourself in one ability. However, you leave another ability severely lacking. For instance, you exercise to improve your strength, however you leave little time for reading, lowering your intelligence.
Gain +1 to an ability score of your choice, and its maximum score increases by 2. Another ability score of your choice decreases by 2, however.
You may take this feat up to 3 times, choosing different abilities each time.