Can you reroll the dice on the same roll two or more times?

Question

Few days ago, our hoity-toity halfling tried (yes, again!!) to impress people around him with his educated manners, his glamorous hat, his luxurious vest, pants and boots, his swanking jewelry and his charming smile. But, this time, another player wanted to be fun and cast a Grease spell, to take the wind out of the halfling's sails.

The halfling has the Lucky racial trait, and also 2 uses of the Indomitable trait. Although he made the save, the player declared he could reroll the dice several times, activating the indomitable two times in the same roll, and more times if any rolls are a '1', because he could also use the Lucky trait. But, will he really be able to repeat the roll more than one time?. Assume he need a 10 in the dice roll to make the save.

• For example, if he get a '1' and he reroll using the Halfling Luck, getting another '1'. Will he be able to reroll the second '1' using again the Halfling Luck?
• If he get a '2'(fail) and spend a use of the Indomitable trait, getting a '3'(also a fail). Will he be able to spend another use of the Indomitable trait to reroll again?
• If he rolls a '1' and reroll the save using the Halfling Luck, getting a '2'(fail). Will be able to spend a use of the Indomitable trait to reroll again? and the opposite?

Now, the GM said the halfling had disadvantage in the saving throw, because he not only tried not to fall, but also to do it without losing his composure. It seems that a reroll let you to repeat only one dice, not both.

• In case he rolls, for example, a '1' and a '2'(a fail) in the two dices. Can he rerroll the 1 (using his Lucky racial trait) and the other dice (using the Indomitable trait)?

Answer 1

When you have advantage or disadvantage and something in the game, such as the halfling's Lucky trait, lets you reroll the d20, you can reroll only one of the dice. You choose which one.

If you roll a 1 you can use the Lucky trait to reroll that die.

Beginning at 9th level, you can reroll a saving throw that you fail. If you do so, you must use the new roll

If you fail the saving throw (with or without triggering Lucky) you can still only reroll one dice because the first quoted rule applies to this too. This can also trigger Lucky but not if the first roll did - that would be using Lucky twice on the same roll.

For your specific example, the 1 would trigger a reroll for Lucky. As this is free there is no reason not to use it. Irrespective of the reroll the 2 is almost certainly cause a failed save. Based on the reroll, you could then decide if spending Indomitable was a good investment.