Zamriel wants you to equip your creatures to make them indestructible during your turn, so being able to cast equipment spells at instant speed and attach them to your creatures when they enter the battlefield makes Sigardas Aid feel like an essential card
Tapping creatures to pay for a convoke spell doesn't change its mana value
Check Lands Check lands dont cause you damage a la shock and pain lands, but they have another requirement
The technology has thankfully been repurposed
You may want up to 40 spells if youre running a spellslinger deck with a commander like Niv-Mizzet, Parun
And that hasnt ended, we just flavor stuff after planeswalkers (Jace's Erasure, Liliana's Specter, Chandra's Ignition) or still after legendary creatures (Ezuri's Predation, Daxos's Torment, Kalemne's Captain, Gisa's Bidding, Geralf's Masterpiece, Oona's Grace, etc)