Battle Mammoth — ruling 1

Battle Mammoth's triggered ability resolves before the spell or ability that caused it to trigger. It will resolve even if that spell or ability is countered.

Battle Mammoth — ruling 2

If a spell or ability an opponent controls targets a single permanent you control more than once, Battle Mammoth's triggered ability will trigger only once. However, if a spell or ability an opponent controls targets multiple permanents you control, Battle Mammoth's triggered ability will trigger once for each of those permanents.

Battle Mammoth — ruling 3

You choose whether to draw a card as Battle Mammoth's triggered ability is resolving.

Battle Mammoth — ruling 4

Because exiling a card with foretell from your hand is a special action, you can do so any time you have priority during your turn, including in response to spells and abilities. Once you announce you're taking the action, no other player can respond by trying to remove the card from your hand.

Battle Mammoth — ruling 5

Casting a foretold card from exile follows the timing rules for that card. If you foretell an instant card, you can cast it as soon as the next player's turn. In most cases, if you foretell a card that isn't an instant (or doesn't have flash), you'll have to wait until your next turn to cast it.

Battle Mammoth — ruling 6

If you're casting a foretold card from exile for its foretell cost, you can't choose to cast it for any other alternative costs. You can, however, pay additional costs, such as kicker costs. If the card has any mandatory additional costs, those must be paid to cast the spell.

Battle Mammoth : règles, fonctionnement et interactions (MTG)

Battle Mammoth is one of those cards players keep asking about. Here is, in plain words, what its official text says, the rulings published by Wizards of the Coast, and the combos players actually run.

Official card text

Trample Whenever a permanent you control becomes the target of a spell or ability an opponent controls, you may draw a card. Foretell (During your turn, you may pay and exile this card from your hand face down. Cast it on a later turn for its foretell cost.)

How it works : Battle Mammoth

Original English text — Wizards of the Coast / Scryfall

#1February 5, 2021· Wizards of the Coast
Battle Mammoth's triggered ability resolves before the spell or ability that caused it to trigger. It will resolve even if that spell or ability is countered.
No other card is named in this ruling.
#2February 5, 2021· Wizards of the Coast
If a spell or ability an opponent controls targets a single permanent you control more than once, Battle Mammoth's triggered ability will trigger only once. However, if a spell or ability an opponent controls targets multiple permanents you control, Battle Mammoth's triggered ability will trigger once for each of those permanents.
No other card is named in this ruling.
#3February 5, 2021· Wizards of the Coast
You choose whether to draw a card as Battle Mammoth's triggered ability is resolving.
No other card is named in this ruling.
#4February 5, 2021· Wizards of the Coast
Because exiling a card with foretell from your hand is a special action, you can do so any time you have priority during your turn, including in response to spells and abilities. Once you announce you're taking the action, no other player can respond by trying to remove the card from your hand.
Card named in this ruling
Foretell
#5February 5, 2021· Wizards of the Coast
Casting a foretold card from exile follows the timing rules for that card. If you foretell an instant card, you can cast it as soon as the next player's turn. In most cases, if you foretell a card that isn't an instant (or doesn't have flash), you'll have to wait until your next turn to cast it.
Card named in this ruling
Foretell
#6February 5, 2021· Wizards of the Coast
If you're casting a foretold card from exile for its foretell cost, you can't choose to cast it for any other alternative costs. You can, however, pay additional costs, such as kicker costs. If the card has any mandatory additional costs, those must be paid to cast the spell.
Card named in this ruling
Foretell