If one target of an escalate spell becomes illegal, the other targets will still be affected. If all of the targets become illegal, the spell won't resolve.

If two of the chosen modes of an escalate spell target a creature, you may choose the same creature for each mode's target, or choose different creatures. The same is true if the chosen modes target a player (or opponent).

If you choose the first and third modes, and destroying the creature ends an "exile until" effect (such as that of Lunarch Inquisitors), the creature will return to the battlefield before you put +1/+1 counters on creatures. The same is true if you choose the second and third modes and destroying the enchantment ends such an effect.

You choose all of your modes at once. You can't wait to perform one mode's actions and then decide to choose more modes.

You can't choose any one mode multiple times.

If an effect allows you to cast a spell that has escalate without paying its mana cost, you pay escalate costs for that spell if you choose more than one mode.

You can tap any untapped creature you control to pay the escalate cost, including one you haven't controlled continuously since the beginning of the turn.

Additional costs don't affect a spell's mana value.

Effects that reduce the cost of spells reduce the total cost, including any escalate costs added.