Unlike something like Starting Town, you cant turn off the life loss at any point unless you just stop using it
Decidueye EX takes advantage of being able to hit with only 1 Energy and then using Cyrus to punish the damaged opponent with its 2 Energy attack
Youre aiming to choose a creature to be exiled, otherwise the exiled card is wasted
A reasonable approximation of the expected power of gold cards is that your 2nd colour of mana adds about a 1/3rd of a mana, the 3rd colour adds 2/3rds of a mana and the fourth is a whole extra mana
To be fair this does work in the TCG to some extent, just compare the current price for a Secret Illustration Rare Iono to the price one commanded at release date (or if you want to be completely insane, during prereleases)
The card is a subset tutor (of sorts) from a very unpopular set, so I like it as a low-risk long-term hold