Creatures like Gelectrode, Walking Ballista, and even Mayhem Devil instantly become deadly when given deathtouch
As loops get more complicated, the chance of making a mistake gets higher, and it's more and more important to be very clear about everything that's happening, ideally keeping track on a notepad for the first iteration in order to make sure you haven't missed anything
The one big change I could see is to switch up the exact merfolk that you choose
You're paying Hill Giant mana for a creature with just half the combined power/toughness
Herald's Horn Herald's Horn is yet another rock that only fits in creature-heavy typal decks but, as one of the best typal support cards, it indeed fits like a glove in those
The Accept header must be present, but you can provide a generic preference