You can tap any untapped legendary creature you control, including one you haven't controlled continuously since the beginning of your most recent turn, to pay the cost of Relic of Legends's activated ability
A couple of tutors like Personal Tutor and Scheming Symmetry ensure you have whatever cards you want to cast perhaps Expropriate to get some extra swings in, Breach the Multiverse to build an imposing board state, or Mnemonic Deluge for an encore of your greatest hits
Niv-Mizzet, the Firemind and Nivix Guildmage card draw and damage engines that fuel your hand and board presence
You get the best deals when you look in a variety of places, but you can also just use a couple of them if youre strapped for time
The Veloci-Ramp-Tor deck does come with a few good reprints too, including the versatile Akroma's Will, Xenagos, God of Revels, a god that turns one of your creatures into a massive threat, and the fighting machine that is Apex Altisaur with its enrage ability