- "This card cannot be used as a Synchro Material Monster" is a condition, not an effect. It also applies in your hand, so you can't use Ronintoadin as a Synchro Material Monster with Eccentric Boy either.
- The text "This card cannot be used as a Synchro Material Monster." of "Ronintoadin" is not treated as an effect of an Effect Monster.
- Removing from play one "Frog" monster from your Graveyard is a cost to activate the effect of "Ronintoadin" which Special Summons it.