Notes & Combos
This is pre-banlist, and heavily inspired by the player who used pendulum magicians to top in Japan tourneys. Main combos revolve around astrolooping to set up crazy boards and getting celestial magician on the board with a synchro monster to play around nibiru and any other handtraps that might come up. you have good back-ups if you get ashed or maxx C'd with abyss dweller pass or masquerena+another body pass. the supreme king synchro and borreload are also flex spots so if you think of something better feel free to alter as it won't effect plays .

Can I ask how dimension shifter work with pendulums, do they just go the extra deck still or straight to banish

Pendulum monsters are banished.
Pendulum monsters go to the Extra Deck face-up instead of the GY but since Shifter states that "any card sent to the GY is banished instead", Pendulum monsters won't go to the Extra Deck because they attempt to go into the GY at first and thus being overridden by Shifter's effect, pendulum monsters get banished instead. The same ruling applies to Macro Cosmos, Dimensional Fissure and other similar cards.

It could be when used on opponent's turn and there are no cards in his GY and the opponent doesn't have CBTG. He's also using Dweller for shutting down GY effects just in case it doesn't work, I guess. Aside from the other omni-negates and disruption on his board when done correctly. Shifter can also be used as a Link material (especially for Selene) and as a Synchro material for Borreload and Baronne just in case Harmonizing gets Ash'd.
But yep, having a replay with this deck in action would be better to see ~

will post replays soon for people who are still interested. Trion Caduceus already answered the question about how shifter interacts with pendulums. You can D Shifter at the start of your combo if you open with it but that will lock you out of astrolooping. You can also do my preferred method which uses d shifter right before you summon selene as your graveyard should be empty at that point and you will have searched d shifter from timestar.