Creeping Tar Pit — ruling 1

A land that becomes a creature may be affected by "summoning sickness." You can't attack with it or use any of its {T} abilities (including its mana abilities) unless it began your most recent turn on the battlefield under your control. Note that summoning sickness cares about when that permanent came under your control, not when it became a creature.

Creeping Tar Pit — ruling 2

When a land becomes a creature, that doesn't count as having a creature enter. The permanent was already on the battlefield; it only changed its types. Abilities that trigger whenever a creature enters won't trigger.

Creeping Tar Pit : règles, fonctionnement et interactions (MTG)

Creeping Tar Pit 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

This land enters tapped. : Add or . : Until end of turn, this land becomes a 3/2 blue and black Elemental creature. It's still a land. It can't be blocked this turn.

How it works : Creeping Tar Pit

Original English text — Wizards of the Coast / Scryfall

#1March 1, 2010· Wizards of the Coast
A land that becomes a creature may be affected by "summoning sickness." You can't attack with it or use any of its abilities (including its mana abilities) unless it began your most recent turn on the battlefield under your control. Note that summoning sickness cares about when that permanent came under your control, not when it became a creature.
No other card is named in this ruling.
#2March 1, 2010· Wizards of the Coast
When a land becomes a creature, that doesn't count as having a creature enter. The permanent was already on the battlefield; it only changed its types. Abilities that trigger whenever a creature enters won't trigger.
No other card is named in this ruling.