This is a ridiculously strong effect if you can willingly put this in the graveyard, since you can permanently haste your entire board for the rest of the game assuming there's no graveyard hate at the table
You're free to go into any of the traditional Assault Mode bosses or summon something new like Junk Warrior/Assault Mode
For example, if I target my own Phyrexian Missionary with Deadly Derision MTGA asks, Hey, dude, are you, like, totally sure you wanna do that!? Probably not a bad idea to leave this option On if you're new to MTGA (or playing while tired/bottle-feeding/otherwise distracted), but a lot of times what youre trying to do does make sense, so turn it off if you find Arena second-guessing you too much
So what are the most valuable versions of Donald in the game
[1] During your Main Phase: You can take 2 "Thunder of the Sacred Beasts" from your hand, Deck and/or GY, and place them face-up on your field, then you can reveal 1 Level 10 "Sacred Beast" monster in your hand, then if you did, take 1 "Fallen Paradise of the Sacred Beasts" from your Deck and place it face-up in your Field Zone