Okay well, right away with Felidar Guardian this goes infinite
Still, adding in sweepers (especially cards like Earthquake and Star of Extinction that take advantage of Sevinne, the Chronoclasm's damage-prevention ability) can greatly improve the deck, and there are some interesting ways to cast cards from our graveyard, like Snapcaster Mage, Mission Briefing and Torrential Gearhulk
Llanowar Elves would be a nice mana producing creature, but I may use ramp spells like Rampant Growth that add more lands to the field while filling my graveyard as they were one time use spells
There's no easy way to load your opponent up on one shot with Toxic, as they will both take regular damage as well as get the set number of counters from the Toxic ability
Elsa also exerts up to 2 characters when entering play, and they dont ready at the start of their owners next turn