If the defending player is your only opponent, no tokens are put onto the battlefield.

Although the tokens enter the battlefield attacking, they were never declared as attackers. Abilities that trigger whenever a creature attacks won't trigger, including the myriad ability of the tokens. If there any costs to have a creature attack, those costs won't apply to the tokens.

Neither "Time" nor "Lord" are creature types. Some older cards were printed with the subtype "Lord," but all of those cards have updated Oracle card text that removed that type.

You choose whether each token is attacking the player or a planeswalker they control as the token is created.

Notably, the part of myriad that makes you exile the creature tokens at end of combat is a triggered ability. This means that the ability will trigger, but you won't exile the tokens when it resolves. Since the tokens also have myriad, attacking with each of them will cause that myriad ability to trigger, causing the Master to, well . . . multiply.

The term "defending player" in the myriad rules (or any other ability of an attacking creature) refers to the player the creature with myriad was attacking at the time it became an attacking creature this combat, or the controller of the planeswalker or the protector of the battle the creature was attacking at the time it became an attacking creature this combat.

If an effect instructs you to choose a creature type, you may choose Time Lord.

The token creatures all enter the battlefield at the same time.

If myriad creates more than one token for any given player (due to an effect such as the one Doubling Season creates), you may choose separately for each token whether it's attacking the player or a planeswalker they control.

Any enters-the-battlefield abilities of the copied creature will trigger when the token enters the battlefield. Any "as [this permanent] enters the battlefield" or "[this permanent] enters the battlefield with" abilities of the copied creature will also work.

Each token copies exactly what was printed on the original creature and nothing else. It doesn't copy whether that creature is tapped or untapped, whether it has any counters on it or Auras and Equipment attached to it, or any non-copy effects that have changed its power, toughness, types, color, and so on.

Unlike other creature types in Magic that are each only one word, the two words "Time Lord" represent a single creature subtype. Time Lord is the only two-word creature type.

If, while you control The Master, Multiplied, you also control a token legendary permanent and a single nontoken legendary permanent with the same name, the legend rule will not cause you to put either one into your graveyard.