Sigardian Paladin — ruling 1

Sigardian Paladin's first ability applies as long as you put a +1/+1 counter on a permanent this turn and that permanent was a creature at the time you put the counter on. It doesn't matter if that creature later left the battlefield, lost its counters, or somehow stopped being a creature.

Sigardian Paladin — ruling 2

Sigardian Paladin's last ability can target only a creature with a +1/+1 counter on it. Once that ability has resolved, the creature has trample and lifelink until end of turn even if it somehow loses its counters or stops being a creature (although trample doesn't help a noncreature permanent much).

Sigardian Paladin : règles, fonctionnement et interactions (MTG)

Sigardian Paladin 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

As long as you've put one or more +1/+1 counters on a creature this turn, this creature has trample and lifelink. : Target creature you control with a +1/+1 counter on it gains trample and lifelink until end of turn.

How it works : Sigardian Paladin

Original English text — Wizards of the Coast / Scryfall

#1November 19, 2021· Wizards of the Coast
Sigardian Paladin's first ability applies as long as you put a +1/+1 counter on a permanent this turn and that permanent was a creature at the time you put the counter on. It doesn't matter if that creature later left the battlefield, lost its counters, or somehow stopped being a creature.
No other card is named in this ruling.
#2November 19, 2021· Wizards of the Coast
Sigardian Paladin's last ability can target only a creature with a +1/+1 counter on it. Once that ability has resolved, the creature has trample and lifelink until end of turn even if it somehow loses its counters or stops being a creature (although trample doesn't help a noncreature permanent much).
No other card is named in this ruling.