Compulsary Escape Device, that bad rare card from REDU
The one that makes each player return one monster to their deck.
What uses does it have?
Well, the obvious one is Madolche. By returning a card to your deck, your ticket allows you to get the advantage lost right back
What about Phantom Skyblaster?
You can either return the skyblaster itself to the deck and re-use the effect, lifting the "Cannot Attack" on the token, or return the token, losing no advantage
And E-Hero Wildman.
Summon him, and target him on resolution to return nothing and have the opponent fly back to the deck
Core Chimails can use the overpowered Urknight to special summon a card once a turn, then return it to stop it from self destructing.
On the topic of Core Chimails, have you tried using the new Flame Dances with them?
Activate Tenki, search Urknight. Summon Urknight, pull out a Crusader by revealing the Iron core.
You now have 2 level 4s at 2100 and 2000 respectively, at the cost of 1 card.
Not enough Continuous spells in your hand for Ice? No Beast Warrior for Urknight and Crusader?
Overlay! Make a Rank 4 exceed.