It's an excellent source of card advantage in your manabase if you're playing at most one, maybe two colors, and it can fill in gaps for colors that don't have unmitigated access to card draw
Whats even better is that even if your spell is countered, you can still draw that extra card
Creature Enchantment - Nightmare Mystic Remora Cumulative upkeep (At the beginning of your upkeep, put an age counter on this permanent, then sacrifice it unless you pay its upkeep cost for each age counter on it.) Whenever an opponent casts a noncreature spell, you may draw a card unless that player pays
I dunno, I don't see what the use of this is unless you're somehow looping it with itself and generating infinite mana
Card Back A good way to signal to everyone youre playing with a proxy deck is to have an alternative card back for all the proxies in your deck, or at least a different card back than an original MTG card
Reliquary Tower and Ajani's Welcome seem to be just good enough to see some play in Commander, and that might just be enough