Now, you are truly worthy of the power of the world's greatest Villain. For starters, not only is your initial stockpile of Quirks increased to twenty-five, but your Quirks are now all connected, woven into an intricate living network: As you use and combine them in different ways, they will 'ping' off of each other, filling in their gaps with adaptations and enhancements better than if you simply trained them alone. While they won't ever truly blend together into a single cohesive unit, they'll be so optimized and fine-tuned that they may as well behave like one.
In addition, as your Quirks strengthen and evolve, not only will they adapt and mutate to become better, but they will also quite literally grow, forming 'buds' of a sort both by themselves and with other Quirks, which will eventually bloom into fully-fledged Quirks of their own with abilities based on those of their 'parents'. Bear in mind however that this is a very slow process, taking at least one or more years for new Quirks to fully form, though this budding can potentially occur for every Quirk in your collection.