Whenever a creature has four or more fuse counters on it, remove all fuse counters from it and destroy it
Take a look at Dark type-shifted Charizard and other Pokmon from upcoming Obsidian Flame card set A fiery Eiscue is among the odd Tera-type cards
This stands true even for competitive Magic
In a singleton format you have to run a set of cards that all fulfill the same basic function, so instead of running 4 copies of Harmonize, you might run Harmonize, Greater Good, Beast Whisperer, Return of the Wildspeaker, Garruk, Primal Hunter, Shamanic Revelation, Soul's Majesty and Rishkar's Expertise
Thats in stark contrast to your game one plan, where youd normally expect to be throwing down discard as fast as possible to get some trade while its relevant
It is likely that cards from those two blocks will be included in the cards that are added to MTG Arena for Historic play