Hydro-Man, Fluid Felon

The design trick is the nightly phase change: at the beginning of your end step, the body loses its creature type and becomes a land that taps for blue, so between turns there is no creature on the battlefield to target. That does two things at once. It sidesteps sorcery-speed removal and board wipes that resolve on an opponent's turn, since the thing an opponent wants to kill is a land until your next untap; and it turns a two-drop into a color-producing permanent that never sits dead, adding a blue mana each cycle without eating a land drop. The catch is that the transformation is not optional. It fires every one of your end steps whether you want the mana or not, so while he is a land he cannot attack, block, or trigger anything keyed off creatures. What you control is not the trigger but the spells around it: the +1/+1 clause only fires when he is a creature at the moment a blue spell goes on the stack, which rewards a deck casting blue on its own turn rather than splashing him alongside off-color spells. Everything about him keys to being untapped into a body at the start of your turn, growing through the turn, then dissolving back into mana at its end. It is an elemental whose flavor sits directly in the rules: a felon who slips through your fingers, hard to kill precisely because he spends half his life as something you cannot fight.