Menace is nice on pretty much any card.
Time Walk is just an incredibly cheap card (to cast anyway)
You should also add repeatable ways to proliferate, like Inexorable TideInexorable Tide, Contagion ClaspContagion Clasp, and Staff of CompleationStaff of Compleation
Giratina V Alternate Full Art 91 / 100 Quick take The top chase card from Lost Origin Powered one of the most dominant competitive decks in format history Artwork by Shinji Kanda is widely considered among the best in modern TCG Rare case where competitive and collector value aligned Collector's readWhat it means for your master set Set landscapeWhere this card sits in Lost Origin white ring = this card VariantsCard variants Holofoil 186/196 $858.75 the only variant this card was printed in (no reverse holo or special pattern), so a master set needs just this one copy
Mega Pokmon can also be basic Pokmon, such as Mega Absol, to shake up gameplay somewhat
I know you said that discarding's a large enough cost as it is, but honestly, it would be vicious to not put an OPT clause