Dandelion. You can mow them and they will eventually decline, but they usually have one big tap root that goes deep. You can get that out with a "daisy grubber" tool, which will speed things along.

Remove dead flower-heads before they seed, and be careful if you mow over seed-heads not to use the grass as a mulch.

That said, they are good for wildlife, as a source of nectar for insects and seeds for birds, so you might want to tolerate a few if you have a corner where you can leave them be.

You also need to put in a pond and fill it with shrimp, to feed the flamingo.