Dreamwinder
{3}{U}
Creature -- Serpent
4/3
~this~ can't attack unless defending player controls an Island.
{U}, Sacrifice an Island: Target land becomes an Island until end of turn.
Floodchaser
{5}{U}
Creature -- Elemental
0/0
~this~ enters with six +1/+1 counters on it.
~this~ can't attack unless defending player controls an Island.
{U}, Remove a +1/+1 counter from ~this~: Target land becomes an Island until end of turn.
Streambed Aquitects
{1}{U}{U}
Creature -- Merfolk Scout
2/3
{T}: Target Merfolk creature gets +1/+1 and gains islandwalk until end of turn. (It can't be blocked as long as defending player controls an Island.)
{T}: Target land becomes an Island until end of turn.