I can do infinite Kroxa in the decklist I've currently got using Nim Deathmantle (and even without infinite, Deathmantle lets me double or triple up on Kroxa's ETB), although my only means of getting enough colorless mana to do it infinitely is Ashnod's Altar with a persist or undying creature, and the only creatures currently in the list that naturally have persist or undying are Geralf's Messenger and Murderous Redcap, so at that point I wouldn't need Kroxa. But I do have Mikaeus, the Unhallowed to give any non-human undying, so could go infinite with Kroxa that way. (And Mikaeus doubles my Kroxa ETB without having the combo available, too.)
Every end step, Kroxa ETB trigger. Add cheap/repeatable reanimation, perhaps a "Players can't draw cards" effect or two...
Heck, if you've got a decent amount of instant-speed reanimation, Lantern of Insight could turn it into a Lantern Control deck, where you decide whether to let them do anything with the card they draw each turn.
Im looking for some synergy cards though, cards with effects like Equilibrium but instead of cast trigger to return creatures, I need ETB triggers so I can bounce these titan back before resolving the ETB trigger.
There is no such effect that will let you have a creature bounce itself. Cloudstone Curio and creature(s) with flash would work, though.