Whilst you're doing these solo gates, you'll also unlock more structure decks, cards, and gems for purchasing card packs, the last of which you'll need later
A great way to take advantage of this is, of course, by using persist creatures, where the counter counteracts the persist ability while also buffing the rest of your creatures
If you really want to commit to the Sirens Call and Angels Trumpet idea, you can springboard off the Mandate of Peace idea and just play Peacekeeper and other cards that prevent creatures from attacking
While mana intensive, the ability to repeatedly refute an opponent's turn by bouncing their guy combined with the ability to use Disappear as a way to "protect" your creatures in combat (cast Disappear on it and then attack freely, knowing you can save it from lethal damage) made for a very potent enchantment that acted more as a sorcery than an enchantment