Teleportal — ruling 1

If you don't pay the overload cost of a spell with overload, that spell will have a single target. If you pay the overload cost, the spell won't have any targets.

Teleportal — ruling 2

Because a spell with overload doesn't target when its overload cost is paid, it may affect permanents with hexproof or with protection from the appropriate color.

Teleportal — ruling 3

To determine the total cost of a spell, start with the mana cost or alternative cost you're paying (such as an overload cost), add any cost increases, then apply any cost reductions. The mana value of the spell remains unchanged, no matter what the total cost to cast it was.

Teleportal — ruling 4

If you are instructed to cast a spell with overload "without paying its mana cost," you can't choose to pay its overload cost instead.

Teleportal — ruling 5

The set of creatures that gets +1/+0 from an overloaded Teleportal is determined as the spell resolves. Creatures you begin to control later in the turn won't get +1/+0. However, because the second part of Teleportal's effect doesn't change the characteristics of any permanents, the set of creatures that can't be blocked is constantly updated. Any creature you control at the moment blockers are chosen can't be blocked.

Teleportal : règles, fonctionnement et interactions (MTG)

Teleportal 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

Target creature you control gets +1/+0 until end of turn and can't be blocked this turn. Overload (You may cast this spell for its overload cost. If you do, change "target" in its text to "each.")

How it works : Teleportal

Original English text — Wizards of the Coast / Scryfall

#1January 12, 2024· Wizards of the Coast
If you don't pay the overload cost of a spell with overload, that spell will have a single target. If you pay the overload cost, the spell won't have any targets.
No other card is named in this ruling.
#2January 12, 2024· Wizards of the Coast
Because a spell with overload doesn't target when its overload cost is paid, it may affect permanents with hexproof or with protection from the appropriate color.
No other card is named in this ruling.
#3January 12, 2024· Wizards of the Coast
To determine the total cost of a spell, start with the mana cost or alternative cost you're paying (such as an overload cost), add any cost increases, then apply any cost reductions. The mana value of the spell remains unchanged, no matter what the total cost to cast it was.
No other card is named in this ruling.
#4January 12, 2024· Wizards of the Coast
If you are instructed to cast a spell with overload "without paying its mana cost," you can't choose to pay its overload cost instead.
No other card is named in this ruling.
#5March 14, 2017· Wizards of the Coast
The set of creatures that gets +1/+0 from an overloaded Teleportal is determined as the spell resolves. Creatures you begin to control later in the turn won't get +1/+0. However, because the second part of Teleportal's effect doesn't change the characteristics of any permanents, the set of creatures that can't be blocked is constantly updated. Any creature you control at the moment blockers are chosen can't be blocked.
No other card is named in this ruling.