Yet another 'help me fix this card' thread

[(nameless one)]

Alright,

I've made a couple of posts here before about my playgroup's custom Cube Draft.

Its my turn and I have a new card idea (which is essentially a rip-off of Time Vault that cannot be broken with Tezz):

Chronoreliquat (4)

Artifact

Chronoreliquat enters the battlefield tapped.

{tap}: Take an extra turn after this one.

Whenever Chronoreliquat becomes untapped, end the turn (Exile all spells and abilities on the stack, including this card. The player whose turn it is discards down to his or her maximum hand size. Damage wears off, and "this turn" and "until end of turn" effects end.)

Would it be broken for Limited? If it saw print, would it be banned in Legacy? How would you guys fix it?

[Jeff Kruchkow]

Still seems broken with Voltaic Key. Play on your turn, end their turn at instant speed and then go twice, rinse and repeat.

If you get to drop it with Key out it's a chant walk that gets you two turns in a row

Play Chronowhatever
In their upkeep untap it
Take your turn.
In their upkeep put extra turn on stack, end their turn.
Go twice.
Repeat.

[Meekrab]

tap, pay half your life: take an extra turn.

tap, exile the top 15 cards of your library: take an extra turn.