Curses are fun for the controlling player, but control in commander is a tricky path that is difficult to manage since some players take it personally
Old One Eyes ability to go from graveyard to hand at the cost of discarding cards makes it right for a reanimator deck, like with Old Stickfingers, getting the exact creatures you want into the yard
While some of these cards, individually, will only cost you a few cents, there are those out there that may require you to break open any spare piggy banks you have lying around
Think of the possibilities
The sheer card advantage Tiamat creates on ETB is well worth it on its own, but its also one of many Food Chain combo enablers that you can put in the command zone
"[Type]cycling [cost]" means "[Cost], Discard this card: Search your library for a [type] card, reveal it, put it into your hand, then shuffle." This type is usually a subtype (as in "Mountaincycling") but can be any card type, subtype, supertype, or combination thereof (as in "basic landcycling")