MArcomage

I would suggest to replace neighbouring cards with non-common Titan and summon Completion ritual

IMO it will be overpowered for the cost as it is now.
But I must admit it is interesting idea.

what about a titan keyword?

So you'll need 7 Titan cards in hand, 2 of which are rare, to win? Titan victory isn't easy at this moment, and another Titan will make it very hard.

Agreed, you cannot add Titan to any more cards, no matter how much sense it might seem to make. Titan victory requires ALL Titan cards. It already requires 6 of the 8 slots in your hand. Just... no.