https://www.reddit.com/r/EDH/comments/9ol5tu/its_finally_finished_my_tribal_tribal_deck_helmed/

http://tappedout.net/mtg-decks/29-09-18-tribal-tribal/?cb=15

https://www.reddit.com/r/CompetitiveEDH/comments/af3pjw/reaper_kingarcane_adaptation_etbs/

AmniO2 archetype video:
https://www.youtube.com/watch?v=dTwSSVPtklQ

Win Conditions:

Reaper King+Changeling Berserker+Changeling Titan+Changeling Hero- Champion Changelings loop with Reaper King out to destroy an arbitrary number of permanents, 99% percent of the time there's no coming back from this for your opponents. Extra consistent too because up to two of the Champion Changelings can be replaced with Clones and the combo still works

Liliana's Contract- Sometimes you just get this to stick with four Changelings out and win, or you could Flash the fourth one in with Didgeridoo on EOT before your Upkeep. On a side note, the ETB of this enchantment isn't nothing either, draw 4 lose 4 is a pretty good deal

Ulamog, the Infinite Gyre- sacrifing Reaper King to Birthing Pod on curve and tutoring this guy into play straight up ends games before they even start

Godo, Bandit Warlord+Helm of the Host- Not an original combo to be sure, but the individual pieces are useful to the deck so it deserves mentioning (Godo untaps our Changelings and tutors Helm/Blade/Boots as needed, and Helm of the Host+Reaper King should be self-explanatory)

General Bombs:

Rite of Replication- Kicked targeting Reaper King this card reads "destroy 25 target permanents" (even better if the target was a non-legendary token of Reaper King created by Helm of the Host)

Kindred Summons- With a mass of Changelings on board, or a Mirror Entity this card is almost like an instant-speed Genesis Wave, that should be enough to explain why its a bomb.

Notorious Throng- if you can get a good clean hit in to trigger the Prowl on this card it can be absolutely brutal, dropping Shared Animosity or Coat of Arms on your next turn can end the game real quick. Also, this card can function as a one sided board wipe with a Time Walk stapled onto it if you have Arcane Adaptation or Xenograft on the board set to Scarecrow with Reaper King out

Kindred Charge- you know what I said about Notorious Throng+Xenograft? well this packs the whole thing into a single card that does it in one turn, sure, you need an established board to make this one worth it, but when it works, it WORKS.

Mirror Entity- this little guy does so much work for this deck, he allows our tribal lords to benefit each other, he makes stuff like the Kindred cards, Peer Pressure, and Whelming Wave even more lopsided than they already are for this deck, and of special note, he can combo with Harabaz Druid to either make a ton of mana really quickly (for casting Rite of Replication or another bomb earlier than expected) or to alpha strike someone (i.e. you have 10 creatures on board, tap {1} to have Mirror Entity make everything 1/1 Changelings, then tap Harabaz Druid for {10}, then pump that {10} into Mirror Entity and now you have 10 10/10's and someone is dying. This card is an all-star in this deck.

[My tappedout.com Link]
https://tappedout.net/mtg-decks/11-01-19-reaper-king-changeling/