Mana Martyr is pretty useless at the moment, but can be a game changer with a L3 Asmodeus and more mana martyr cards in future.
Why? Because a huge mp drain can result into a scenario where the next card is not able to cast his +4 skill (and OHKO the opponent) because it has too little mp left.
Think about that if you have 2 or 3 mana martyr cards in your deck supported by L3 Asmodeus.
And recommendation for your Titania: Leave her at Lvl69 (she learns MM at Lvl70). With MR, -20WIS and +4 Ele she has best OHKO Rate and you do not lose any trade value. Did that with my Titania. If you decide to set up a Mana Martyr Deck later with L3 Asmodeus, you have the opportunity to do so.