ChangelingChangeling is a characteristic-defining ability. “Changeling” means “This object is every creature type.” This ability works everywhere, even outside the game. See rule 604.3. (CR 702.73) (This card is every creature type.)
ChampionChampion represents two triggered abilities. “Champion an [object]” means “When this permanent enters, sacrifice it unless you exile another [object] you control” and “When this permanent leaves the battlefield, return the exiled card to the battlefield under its owner’s control.”
The two abilities represented by champion are linked. See rule 607, “Linked Abilities.”
A permanent is “championed” by another permanent if the latter exiles the former as the direct result of a champion ability. (CR 702.72) a creature (When this enters,
sacrificeTo sacrifice a permanent, its controller moves it from the battlefield directly to its owner’s graveyard. A player can’t sacrifice something that isn’t a permanent, or something that’s a permanent they don’t control. Sacrificing a permanent doesn’t destroy it, so regeneration or other effects that replace destruction can’t affect this action. (CR 701.21) it unless you
exileTo exile an object, move it to the exile zone from wherever it is. See rule 406, “Exile.” (CR 701.13) another creature you control. When this leaves the battlefield, that card returns to the battlefield.)
LifelinkLifelink is a static ability.
Damage dealt by a source with lifelink causes that source’s controller, or its owner if it has no controller, to gain that much life (in addition to any other results that damage causes). See rule 120.3.
If an object is no longer in the zone it’s expected to be in as an effect causes it to deal damage, its last known information is used to determine whether it had lifelink.
The lifelink rules function no matter what zone an object with lifelink deals damage from.
If multiple sources with lifelink deal damage at the same time, they cause separate life gain events (see rules 119.9–10).
Multiple instances of lifelink on the same object are redundant. (CR 702.15) (Damage dealt by this creature also causes you to gain that much life.)