As we said earlier, once a rebalanced card is only playable in Historic, we can balance solely around that
I highly recommend starting with one of these: Solemn SimulacrumSolemn Simulacrum, Skyclave ApparitionSkyclave Apparition, and Whirler VirtuosoWhirler Virtuoso
Abomination of Llanowar Animate Graveyard Apocalypse Demon Bloodsworn Knight Boneyard Mycodrax Boneyard Wurm Candlekeep Inspiration Consuming Aberration Consuming Blob Elephant Resurgence Graveyard Busybody Leonardo da Vinci Lumra, Bellow of the Woods Melek, Reforged Researcher Nethergoyf Old Stickfingers Revenant Seize the Storm Sewer Nemesis Souls of the Lost Splinterfright Sutured Ghoul Svogthos, the Restless Tomb Textbook Tabulator The Capitoline Triad Titania, Gaea Incarnate Umbra Stalker Unlicensed Hearse Urborg Lhurgoyf Wrenn and Seven
There are cards with infect in all four of the creatures colors, making it easy to incorporate them as well as creatures with toxic for a formidable poison counters deck build
Instead of having a color restriction, you can just pay 2 life