Fixes, Dec. 9

BSE:
Black Rock City: Removed 'This is a mana ability and does not use the
stack.' (redundant) Considered broken but I'm keeping it as is. It's
already legendary and mythic.
Black Swan: 'non-land' to 'nonland'
Burrowing Owl: Changed rule text to "Opponents cannot play a land on
their turn unless they pay 1. This effect is not cumulative." in order
to prevent this effect from compounding.
Filter Bubble: Changed 'Vanishing 2' to 'Vanishing 4'
Infinite Game: Removed the 'and any exiled cards' phrase to prevent
brokenness with cards that exile themselves (Black Rock City, for
instance)
Inside the Loop: Cost changed from 2R to 1UR
International Art English: Cost changed from 1BB to 1UB
Keynes's Jetpack: Added Legendary
Manuel DeLanda: Changed rule text to "Instant and sorcery spells cast by
any player cost 1 less to cast." to emphasize that the effect is global.
Morlocks: Replaced 'Vigilant' with 'Vigilance'
PHB: Corrected Clueless text 'Clueless creatures cannot attack or
block.' Added '3T: Target creature becomes clueless until end of turn.
Q: Target creature becomes clueless until end of turn.' to prevent abuse
with Keynes's Jetpack.
Sergey Alexeyevich Lebedev: Added T to activated ability cost to prevent
abuse with Keynes's Jetpack

BSE2
Amanda Palmer: Replaced custom rule text with Convoke
Brandolini's Law: Replaced 'owner' with 'controller'
System D: Added T to activated ability cost to prevent abuse with
Keynes's Jetpack

Note:

Was told to put commons between activation costs, such as R,T:
This is not really possible with MSE.

Keynes's Jetpack possibly broken with:
Janus
PHB
Sergey Alexeyevich Lebedev