Card of the Week Contest #510: Round-Off

I think the last ability is off for both, since payments don't use the stack, so this trigger won't really make sense. What you can do is maybe something like:
"Once per turn per source, you may pay half of any life costs of abilities of sources you control, rounded down."

@Idea: It needs to be a replacement ability, using the "if..instead" wording in your given example.

Xander's Debt Collection 
Sorcery
Each player discards half the cards in their hand, rounded down, mills half their library, rounded down, and sacrifices half the nonland permanents they control, rounded down.

Yes the art is from the official MtG card Wizard's Retort but it's too fitting to not use here.

Picky me:
So my blood token gonna go fast? :-) I assume you forgot "creature" in there :-)
Because you already double it, there should be no need for rounding when you exile half of it -- especially because it only cares about stuff it created itself.

To add to this: incubate tokens. You want those to have haste with this. If you get to flip 'em.

Also, a suggestion about something in the wording of the card: the haste giving might be misconstrued as being for only the doubled half, as that's what I thought at first. Could it not flatout give all your tokens haste? As a seperate rules line. Possibly something like, your tokens have haste, or, tokens that enter under your control gain haste.

Ruleswise your current text is sound, so it's fine to leave it as is. I am mostly concerned about an expectation people have bleeding over into how they read the card: temporary one-turn tokens need haste. This then leads to the conclusion: only the temporary half gets haste. Which was my thought process at first.

It is properly formulated ruleswise though, so you can just as well ignore this suggestion.

Leave it, it's perfect.