Kiki-Jiki can copy creatures, and Zealous Conscripts can untap a permanent when it enters the battlefield. Create a copy of Zealous Conscripts using Kiki-Jiki, untap Kiki-Jiki with the Conscripts' ability, and repeat ad infinitum for an army of hasty Conscripts.

With Mikaeus on the field, Triskelion enters with an additional +1/+1 counter due to undying. Triskelion can remove these counters to deal damage. When it dies with no counters, Mikaeus brings it back with undying, and the loop continues. It's a never-ending game of undead ping-pong!

This combo is a fan favorite in casual and Commander games. Whenever you gain life, Sanguine Bond makes an opponent lose that much life. Exquisite Blood then triggers off that loss, making you gain life equal to the life lost, and so on. It's like a dark magic ping-pong!

Splinter Twin enchants a creature like Pestermite. When the enchanted creature taps, it creates a copy of itself, which can then be tapped to create another copy, and so on. This results in infinite creatures with haste for a lethal attack.

Basalt Monolith taps for three mana but doesn't untap during your untap step. You can untap it for three mana, and with Rings of Brighthearth, you can copy the untap ability. This generates infinite colorless mana, perfect for powering out massive spells or abilities.

Palinchron can untap seven lands when it enters the battlefield. Pair it with Phantasmal Image, copying Palinchron. The copy can untap lands to recast Phantasmal Image, leading to infinite mana and infinite Palinchrons.