He's using his frost breath to turn the mice into ice (aka removing their first letter)
You need less one drop burn cards than you do dorks

0.3%inclusion 12 decks 3.64K decks Happy Hogan, Dauntless Driver 28%inclusion 7 decks 25 decks Invisible Woman 0.3%inclusion 2 decks 648 decks The Scarlet Witch 0.1%inclusion 2 decks 1.48K decks Hawkeye, Master Marksman 1.0%inclusion 1 decks 101 decks Top Commanders Kolodin, Triumph Caster 47%inclusion 1.81K decks 3.83K decks Balthier and Fran 55%inclusion 1.33K decks 2.43K decks Depala, Pilot Exemplar 61%inclusion 993 decks 1.63K decks Edward Kenway 6.1%inclusion 792 decks 13.1K decks Setzer, Wandering Gambler 30%inclusion 528 decks 1.75K decks Captain Rex Nebula 33%inclusion 458 decks 1.39K decks Samut, the Driving Force 9.0%inclusion 427 decks 4.75K decks Kykar, Wind's Fury 1.7%inclusion 231 decks 13.8K decks Breya, Etherium Shaper 0.8%inclusion 180 decks 21.8K decks Pia Nalaar, Chief Mechanic 12%inclusion 154 decks 1.24K decks Optimus Prime, Hero 2.5%inclusion 118 decks 4.72K decks Astor, Bearer of Blades 8.6%inclusion 94 decks 1.09K decks RMS Titanic 8.0%inclusion 91 decks 1.13K decks Dr

Every activation has a chance to put a bunch of lands and non-creature cards to the bottom of your library
Each opponent loses X life and you gain X life, where X is that card's mana value
Going by EDHREC, it seems fans are mainly using Caretaker's Talent alongside new Bloomburrow MTG commanders like Baylen the Haymaker and Finneas