Amoeboid Changeling does not have summoning sickness.
Notable Prerequisites
You control another nontoken creature.
Steps
Activate
Amoeboid Changeling's second ability by tapping it, causing another nontoken creature you control to lose all creature types until end of turn.
Activate
Evereth by sacrificing the creature targeted in step 1.
When the creature dies,
Valkyrie's Call triggers, returning the creature from your graveyard to the battlefield as a white Angel.
When the creature enters the battlefield,
Intruder Alarm triggers, untapping all creatures.
Resolve the
Evereth ability.
Repeat.
Notes
If you have a way to kill
Evereth and available, you can do so after putting a significant amount of +1/+1 counters on it to deal damage to each opponent using its second ability.
Results
Infinite +1/+1 counters on a creature.
Infinite creature ETB.
Infinite creature LTB.
Infinite creature sacrifice triggers.
Infinite death triggers.
Infinite mana creatures you control can produce.
Infinite untap of creatures.
Infinite damage.
Metadata
Bracket tag
ExhibitionBracket 1+
For any deck
1
2
3
4
5
1 · Exhibition5 · cEDH
Bracket tags are estimated from the cards and results of each combo, as a guideline rather than a strict classification.