Does Siphon Power's +1/-1 might effect apply to units that move to the targeted battlefield after the spell resolves?

Ruling: No. Siphon Power is a one-time effect that only applies to units present at the targeted battlefield when the spell resolves. Units that move to that battlefield later are not affected.

Sequence:

• Siphon Power resolves, targeting a battlefield
• The spell identifies which units are currently at that battlefield
• Those units are given +1/-1 might until end of turn
• Units moving to that battlefield afterward do not receive the buff/debuff

Nuances:

• The key word is "give" which is a one-time action that occurs at resolution, not a passive effect
• The effect stays on the units that received it for the duration (until end of turn), even if those units move away from the battlefield
• The battlefield itself does not gain a passive ability; the spell gives the effect directly to the units
• This works the same way as other similar cards like Grand Strategem, Discipline, and Stupify