>Lazav, the Multifarious + Medomai the Ageless
Lazav otb, medomai in the grave. Copy medomai with Lazav, attack, get an extra turn, then you can continue to attack during extra turns since Lazav keep his name. Infinite turns.

>Timestream Navigator + Helm of the Host
Both otb, attach helm on navigator, during attack step you get a copy with haste of Navigator, use the extra turn's ability of the copy to get an extra turn, it get destroyed instead of going to bottom but you don't care since the OG Navigator is still availible to do it again next turn. Infinite turns.

>Sylvan Awakening + Jeskai Ascendancy
Alrdy used in few lists, once your lands are animated, you'll be able to untap them all + pump them at each spell you cast thanks to ascendancy. The advantage compared to previous lists is how hard to answer the combo is, and with 4 or more lands otb you only need few cantrips to have lethal. Kill.

>Crackdown Construct + Wandering Fumarole
Both otb, pay to animate the land, then use the '0 :' ability to swap power/thoughness a thousand time, the construct will get +1/+1 for each time you activated it. Use it after blockers are declared to surprise your opponent making your innoncent 2/2 into an infinite/infinite. Kill.

>Boros Reckoner + Rush of Vitality
Reckoner otb, rush in hand. At any time reckoner would be dealt dmg (blocking/attacking, but you can also shock it or whatever) cast Rush to give him lifelink + indestructible. You then use the triggered ability of reckoner to have the dmg dealt to himself. With the lifelink you'll gain life, but the ability trigger again since he was dealt damage once again. Do it ad nauseam to have infinite life. Pros : this combo is very cheap to setup.

>Fraying Sanity + Traumatize
Fraying otb, cast traumatize to have half the opponent's library milled, fraying will then copy it to put the other half in the grave aswell. Kill by mill.

>Demonic Pact + Harmless Offering
Pact otb, offering in hand. Keep pack until you only have the 'you lose' clause availible, then offer it to your opponent for him to lose at the next upkeep. Kill.

>Possibility Storm + Lavinia, Azorius Renegade OR Teferi, Time Raveler
Both otb, Lavinia/teferi will deny the opponent the storm trigger (no mana for lavinia, instant speed for nog) so he wont be able to cast a single spell for the rest of the game. Hardlock.

>Sigarda's Aid + Colossus Hammer
Both otb, pretty self explanatory : sigarda's aid will save you the equip cost so hammer read : "1 : +10/+10", equip it on a creature with trample/double strike for maximum efficiency. Synergy.

>Narset, Parter of Veils + Day's Undoing
Narset otb, undoing in hand. Cast undoing to have the opponent's hand destroyed while you draw a fresh new 7. Synergy.

>Acrobatic Maneuver + Naru Meha, Master Wizard
Naru otb, maneuver in hand. Cast maneuver targeting Naru, she'll blink then her etb ability will trigger and copy maneuver, you draw 1 then cast the copy targeting Naru once again. You can draw your whole library this way. Infinite draws/etb trigger.

>Prime Speaker Vannifar + Timestream Navigator
You need a creature costing 1 who can be played back from grave for this combo to work (bloodsoaked, gutterbones, dread wanderer). 3 creatures otb, use Navigator's activated ability to get an extra turn, she goes on bottom of the lib. Use then Vannifar, saccing the 1cmc creature to fetch back navigator otb. During your extra turn play the 1cmc creature from grave, use navigator again, then fetch it back with vannifar ad nauseam. The nice thing about this combo is vannifar alone can fetch all the others pieces of the combo. Infinite turns.

>Flood of Tears + Omniscience
You need to have 4 nonlands permanents otb for this combo to work, if possible cheap stuff with etb triggers adding value. Cast flood of tears to bounce both players' board, then thanks to the 4 permanents bounced on your side, cast omniscience for free. You can then recast all the value stuff bounced to get really ahead, and all your spells are now free. Synergy.

>Ornithopter + Crackdown Construct + Lazav, the Multifarious
Orni + construct in your grave, lazav otb. During attack step have Lazav copy the construct for 4, then copy the orni for 0, which will trigger the construct ability on Lazav. You then copy the orni a billion time to have an infinite/infinite Lazav with flying.

>Star of Extinction + Boros Reckoner OR Truefire Captain
Pretty obvious, Star deals 20 to each creature, redirect 20 damage dealt to reckoner/truefire to the opponent's face.

>Possibility Storm + Adventure spells (sorceries only)
Adventure spell in hand (like lovestruck beast), storm otb and Enter the Infinite (need to be the only sorcery beside adventures in your build) + Borborygmos Enraged in your library. Once you have Storm otb, cast the adventure spell for G, the spell get exiled and storm will dig for the next sorcery on your library. But since the adventure spells are only considered sorceries while they resolve and creatures anywhere else, the only target left is enter the infinite. Infinite resolve, you draw your whole library and put back Borborygmos on top. You then cast any creature from your hand (a ballista for 0 usually) and storm will exile it to fetch the only card left in your library : Big Borbo, you then discard a dozen lands you have in hand to Borbo's ability to bolt the opponent to death.