Can you play multiple legendary creatures in Magic the Gathering?

Answer 1

A creature's ability can be used as many times as you can pay it, unless stated otherwise. If a creature has to tap to be able to use the ability, that will mean you need to untap it before you can use the ability again. Some abilities state they can only be used once per turn, others may state they can only be used "at a time when you can use a sorcery" meaning they can only be done in your main phases when no other effects are on the stack.

But in any other case, the creature's effect is instant speed.

Answer 2

You are definitely allowed more than one permanent in play with the 'Legendary' supertype, but if you have two with the same name, then all of those with that name will be sent to the graveyard. Even so though, you can still cast the second one, even though it wiill be sent to the graveyard as soon as it enters the Battlefield.

Answer 3

At almost all times, there is no limit. But if you have more then seven at the end of your end-of-turn step, you must discard down to seven. So imagine if your opponent did something in his turn to make you have 10 cards in hand. You are allowed to keep this many and more, all the way up until the end of your own turn.

Answer 4

infinity

As many as you can before your opponents quit, lol.

Answer 5

There's no hard limit, you can level it up past the point where it has gained its final set of stats and effects, it just does nothing.

Answer 6

Basic lands - as many as you want.

Other cards - 4 maximum, unless stated otherwise on the card (Relentless Rats, for example).