Players can be granted boons depending on the amount of mana used while this mechanic is in effect
Instants are spells you can cast at almost any time
In fact, before I even knew much of anything about all the various formats, I played a Simic deck which was like 80 cards filled with stuff like an Arcanis the Omnipotent with multiple ways to untap it and some other things with useful activated abilities, a playset of Roil Elementals which I protected with counterspells and Archetype of Endurance (they were fun to use alongside Explosive Vegetation and similar effects), Lifeblood Hydra, Horizon Chimera were others, and finally some goodies like Prophet of Kruphix (rip its commander banning) and later additions like Vorinclex, Voice of Hunger
He is quite an all round card offering you some board presence, card advantage and quite a serious threat in the long run on the cheap
Since Eye of Nidhoggs home precon is a fantastic fit for it, there hasnt been an excess of supply to buffer any potential spike
Notably, this card synergizes with Madam Mim Fox, which can pull Merlin back to a players hand so that players can use it to draw even more cards later in the game